344 FXUS66 KSEW 201047 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 247 AM PST Fri Dec 20 2024 .SYNOPSIS...A series of fronts will bring several rounds of light precipitation into tomorrow, with breezy winds and slightly warmer temperatures. A more active pattern is set to evolve and take shape this weekend and last into next week, with an increased chance of impactful weather arriving during the holidays. && .SHORT TERM /TODAY THROUGH SUNDAY/...Showers have largely tapered early this morning as shortwave ridging evolves and will keep things drier through the morning hours. The next front will arrive early in the afternoon and bring back precipitation to the area. The weekend will be damp, with a few frontal systems moving through. On Saturday, expect some breezy east winds through the Cascade gaps in the morning, although high wind is not anticipated. South winds will resume Saturday afternoon but will not be particularly strong. Highs over the weekend will be slightly warmer than average with afternoon highs in the 50s and lows in the 40s. Snow levels will lower somewhat on Sunday for light accumulations at the passes. .LONG TERM /MONDAY THROUGH THURSDAY/...The pattern activity is expected to amplify into next week, with additional systems expected around the holidays. Probabilities in increased atmospheric river activity accompanying these frontal systems have increased as well. A stronger atmospheric river is possible by midweek, lingering into Thursday with higher integrated water vapor values, suggesting more rain and snow in the Cascades and Olympics. In addition to heavy rain at times, there will be periods of stronger winds. The CPC outlooks suggest a moderate risk (generally 40 to 60 percent chance) of heavy rain and mountain snow. The potential exists for implications to busy holiday travel, but it is still somewhat early to get an indication of what those will be, but this will be refined as more is known about the storms on their way in the coming days. Kristell && .AVIATION...Southwest flow aloft will develop this morning as upper level trough digs south offshore and warm front moves by to the west of the area. Offshore flow will continue at the lower levels with E/SE winds generally 5-10 kt. Mainly VFR as cloud cover increases this morning, with areas of fog and low stratus lingering across the Chehalis Valley and along the Strait of Juan de Fuca. Shower activity will lift northward later this morning, with brief MVFR conditions in showers. Conditions will dry from the west through the afternoon and evening hours as showers diminish. Drying overnight will give way to some fog development that may impact the southern terminals Saturday morning. KSEA...VFR ceilings through Friday, with brief MVFR conditions in showers that develop today. Winds generally E to SE 4 to 8 kt through the period. 15 && .MARINE...A series of fronts will cross the region over the next several days, maintaining seas above 10 feet and periods of breezy conditions through the weekend and into next week. A Small Craft Advisory remains in effect for the coastal waters through the early morning, which will continue through the afternoon for the inner coastal waters and Eastern Strait of Juan de Fuca, and will be replaced by a Gale Warning for the outer coastal waters. SCA conditions will continue overnight into Saturday morning, with potential Gale conditions developing later Saturday morning and into the afternoon as a front once again brings in gusty winds over the outer waters and maintains elevated seas. Combined seas this afternoon 10 to 13 feet. Seas will then build upwards to 15 to 19 feet Saturday and are favored to stay elevated in the 15 to 25 foot range through the weekend and into early next week. Seas are favored to ease briefly to 12 to 15 feet Tuesday night into Wednesday before another round of elevated seas 17 to 21 feet the second half of next week. 15 && .HYDROLOGY...Additional incoming precipitation later this week looks to remain light with only minor rises on area rivers expected. The Skokomish River will continue to recede, but remain in the vicinity of flood stage the next few days. The threat of river flooding across western Washington will increase again mid to late next week, with ensembles showing the potential for significant precipitation to return. While discrepancies remain, this may cause an increasing chance of river flooding and landslide concerns that may impact holiday travel. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 6 AM this morning to 3 PM PST this afternoon for West Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 4 AM PST Saturday for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Gale Watch from late tonight through Saturday afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Small Craft Advisory until 6 AM PST early this morning for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory from 3 PM this afternoon to 4 AM PST Saturday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Gale Warning from 6 AM this morning to 3 PM PST this afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. && $$

078 FXUS66 KPQR 201057 AFDPQR Area Forecast Discussion National Weather Service Portland OR 255 AM PST Fri Dec 20 2024 .SYNOPSIS...Rather benign weather today, under mostly cloudy and mild conditions. Then, back to rain, as the first in a series of fronts will push across the region on Saturday. Snow will continue across the high Cascades. Next front arrives on Sunday. Then, a break arrives on Monday, but more rain and mountain snow expected through bulk of next week. && .SHORT TERM...(Today through Sunday)... Mild temperatures this morning across region, with temperatures in the mid to upper 40s, though a few spots holding close to 50. Do have areas of fog and low clouds in the south Willamette Valley, where visibility has been under a mile at times in/around Eugene. That fog will gradually thin and lift to stratus later this am. Main story is the the continued moist and mild southwest flow aloft. Generally, will remain dry across the region today, though may see a few passing sprinkles at times. Otherwise, variable clouds and temperatures in the 50s, with breezy east winds in/near western Columbia Gorge into the east Portland/Vancouver metro area. There is a chance, albeit small, that a few spots along the coast could reach 60 to 62 for highs today. The record warmest ever temperature in December for Astoria is 64 deg (back on 26 Dec 1980). Dry tonight as the region awaits the next front. Will be dry, with variable clouds. Again, could see some spotty fog across the inland valleys. Will see an uptick of the offshore flow, with easterly winds 5 to 15 mph along the coast and across Clark County and North Willamette Valley. But, bit strong in the western Columbia Gorge out across the east Portland/Vancouver metro, where will generally have east winds gusting 30 to 40 mph. More exposed spots in the Gorge likely to have gusts 40 to 50 mph. Next round of rain arrive late tonight into Saturday, with rain to the coast by 6 am, and spreading inland through early to mid Saturday morning. Main surface slow with this front will remain well offshore as it moves towards Vancouver Island. As it does, will push a front to the coast by late morning, with that front moving inland quickly in the afternoon. So, rain will transition to showers behind the front. Rainfall not all that impressive with this system, with most areas getting 0.25 to 0.50 inch, and 0.50 to 1.00 across the Coast Range/Willapa Hills. Not all that concerned about snow, as snow levels remain at or above 6500 ft, with 4 to 8 inches in the higher elevations. As such, passes will remain wet, with just rain. Showers continues Saturday night into early Sunday, But, the next in the series of fronts will arrive on Sunday. Looks to be very wet day, with 0.25 to 0.50 inch for most inland areas, with a 0.50 to 1.00 inch for the coast, and 0.75 to 1.50 inches for the Coast Range and Willapa Hills. At this time this would not cause any flooding, though enough to cause some ponding of water in area with poor drainage, like leaf-clogged drains and low-lying spots. /Rockey && .LONG TERM...(Monday through Thursday)...After a transient ridge on Monday another system likely moves overhead come Tuesday. Afterwards, it`s a rinse and repeat of this pattern with a trough feature moving WSW to ENE into western CONUS every 24-48 hours through the end of the week. Still, models have not settled down enough to pin point details at this time, with differences in strength of the lows, and the eventual storms tracks. If they are farther offshore, or move more northward, then could see less rain and wind. But, if they move closer to the Pacific NW, then more rain and winds could be likely. As of now, just have to go with the overall trends, with some potential of heavy rain (and high elevation snow) for mid to late next week. Finer details like the surface low pressure placement associated with a strong system slated for the Wed/Thu time period will determine our local impacts. For example, river flooding is highly dependent on our rainfall forecast, and the QPF forecast is dependent on the low track. Same goes with determining potential for strong winds. At this time, confidence still remains low to moderate for these impacts. The latest HEFS guidance suggests a 15-35% chance that rivers along the coast/Coast Range reaching flood stage later next week. Snow levels will rain mainly near or above the passes, running 4000 to 7000 feet, the highest snow levels will occur ahead of frontal passages. /Rockey/Alviz && .AVIATION...Conditions are generally VFR across the region early this morning although there are some pockets of patchy fog sloshing around the Tualatin Valley and portions of the Willamette Valley (KEUG). Any fog likely lifts as the morning goes on thanks to increasing mid to high cloud cover. Later this morning into midday hours a decaying frontal boundary is expected to bring a light band of moisture to region, mainly at the coast and between 20-00z. There`s a chance light precipitation makes it to the I-5 corridor but all terminals should just remain VFR. Winds likely stay below 10-15 knots at all sites except for gusty easterly winds at TTD and southerly winds along the coast. PDX AND APPROACHES...VFR CIGs/VIS continues through the TAF period with persistent easterly winds coming from the Columbia River Gorge. Off chance(15-25%) for light rain at times after 20-22z as a weak front passes through, though cigs remain VFR throughout. Not expecting rain to be a prevailing condition so it was excluded from the 12z TAF. -Schuldt && .MARINE...Active conditions continue the next week and beyond as a broad low pressure remains over the NE Pacific steering a parade of frontal boundaries into the coast waters every 24-36hrs. One of these aforementioned fronts is slated to arrive this morning likely bringing Gales to the outer waters through the afternoon hours. After a brief lull, albeit with likely lingering hazardous seas for at least the outer waters, periods of Gales are expected both Saturday and Sunday. Models have backed off slightly for Storm force gusts on Sunday but there`s still an outside chance (20%) for winds to reach into this category. As numerous frontal systems continue to traverse the waters early next week, a large and energetic westerly swell will contribute to large and chaotic seas going forward. Expect seas to remain in the mid to upper teens from Saturday through much of the next week, with seas potentially building into the 20-25 ft range by Monday. Expect the associated with wave periods in the upper teens to near 20 seconds early next week as well. Mariners should be prepared for continued hazardous conditions through the middle to end end of next week. -Schuldt/CB && .BEACH HAZARDS...A large, energetic westerly swell will build over the coastal waters and begin impacting the coastline this weekend into early next week. Seas in excess of 15 to 20 feet with a period of around 20 seconds could result as breaking waves approaching 25 to 30 feet in the surf zone. Thus a High Surf Advisory has been issued for Saturday morning through Monday evening - largest breakers on the latter day. Beachgoers should be prepared for dangerous surf conditions and large waves running far up onto the beach beginning late Sunday and continuing through early next week. -Schuldt/CB && .PQR WATCHES/WARNINGS/ADVISORIES... OR...High Surf Advisory from 7 AM SAT to 10 PM MON for ORZ101>103. WA...High Surf Advisory from 7 AM SAT to 10 PM MON for WAZ201. PZ...Small Craft Advisory today thru tonight for PZZ210. Small Craft Advisory today thru 6 am SAT PZZ251>253. Small Craft Advisory until 6 AM today for PZZ271>273. Gale Warning today from 6 am to 3 pm for PZZ271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland

872 FXUS66 KMFR 201127 AFDMFR Area Forecast Discussion National Weather Service Medford OR 327 AM PST Fri Dec 20 2024 .DISCUSSION...This weekend and through the holiday week is shaping up to be a pretty active period. Persistent upper level troughing will send numerous fronts through the region, bringing periods of gusty/strong winds, moderate to heavy rain and high elevation snow. Snow levels will remain fairly high (6000-7000 ft) through Christmas Eve, so the main impact from these fronts will gusty winds. Snow levels trend lower for the latter half of the week starting Christmas night, so we`ll be monitoring this period for potential winter impacts. The first in the series of active weather is grazing the region this morning. Radar shows some light returns just along the coast and over the marine waters, as well as across central Lake County. So far, none of our observations sites have reported precipitation, but if anything is reaching the ground, it should be fairly light. Overall, this shortwave is largely go unnoticed aside from some increased cloud cover today. Fog and low clouds have filled the West Side Valleys this morning, but this shortwave is keeping fog from getting too dense. Most areas will remain dry through the day today, though low clouds will be stubborn to clear the valleys until the afternoon hours, so there probably won`t be too much sunshine to be had. Starting late tonight and going through Christmas Eve, there will be roughly three shortwaves that pass through the area. The first affects the region late tonight into Saturday, the next arrives late Sunday into Monday, and the next coming late Monday into Tuesday (Christmas Eve). Each of these fronts will bring their own punch of winds as these troughs are negatively tilted, but snow levels will be high during this period so winter impacts will be limited. The first round of strong gusty winds begins this evening and continues overnight into early Saturday morning. Redding-Medford pressure gradients are forecast to be -7 to -9, and this is more than sufficient for winds to reach advisory criteria in the Shasta Valley and even the southern end of the Rogue Valley. Some guidance is even suggesting winds could reach warning levels in the Shasta Valley this evening and overnight. For now, will maintain the current Wind Advisory and let the day shift take a look at the next round of model guidance to decide if any changes are necessary. It will be windy along the coast and east of the Cascades as well, but warning level winds are not anticipated at the coast. The current Wind Advisory covers the gusty winds expected across the East Side, and details can be found at NPWMFR. The front will move onshore late tonight and pass through the area during the morning hours on Saturday. Showers will continue through the afternoon hours, then we`ll see a brief break Saturday night into early Sunday. Snow levels will be up near 6000-7000 ft with the bulk of the precipitation, then lower down to around 5000 ft during the showery period. Winter impacts will be limited the higher peaks with generally 4-6 inches expected with this first wave. Precipitation amounts will range from 0.75"-1.50" along the coast, western and southern Siskiyou County (locally up to 2") to a 0.25"-0.50" for the rest of the area. The next two waves (Sunday night/Monday and Monday night/Tuesday) will be fairly similar scenarios, especially the Sunday night/Monday front. The strongest of these waves, however, will be the Monday into Christmas Eve front. This will bring the most precipitation to the region, but snow levels will once again be high (up around 8000- 9000 ft) with the bulk of the rain. Snow levels do lower down to around 4000 ft behind the front, but then the pattern will be more showery and tapering off. So even with this being the stronger front, winter impacts should be limited to the highest peaks and minimal still after snow levels lower. We`ll likely see another round of strong winds with this front, but current guidance indicates winds should stay below warning criteria. There will be another break in the weather for Christmas Eve night that continues through at least Christmas afternoon. The next front in the series arrives Christmas night, and another wave sometime Friday into Saturday. These fronts bear watching with snow levels hovering around 4000-5000 ft and plenty of moisture heading this way. If the current forecast holds true, we could be looking at another foot or two of snow along the Cascades with potential winter impacts in the Mt Shasta City region as well. Stay tuned for updates as this time draws nearer. /BR-y && .AVIATION...20/12Z TAFS...LIFR fog is in the Rogue Valley, including Medford and Grants Pass and the Umpqua Basin, including Roseburg. These conditions will persist through this morning, then expect improving conditions in the afternoon. Valley LIFR/IFR is expected to develop again this evening, then be disrupted by the next front moving inland during Saturday morning. South/southeast winds will increase towards the end of the TAF period with the passing front. -DW/Hermansen && .MARINE...Updated 230 AM PST Friday, December 20, 2024...Several very strong fronts are expected this weekend into next week with persistent very high and very steep, chaotic, dangerous seas, interrupted by periods of gales. Another front moves through this morning into the evening. Conditions will worsen with strong gusty winds, up to gales, and high and very steep seas developing across the waters. Then, a stronger front arrives tonight and Saturday with gales and very high and very steep, chaotic seas. Additional stronger fronts follow Sunday into early next week resulting in periods of gales and prolonged, very high and very steep seas. Seas will be a mix of short period wind seas and long period swell (with periods of around 14 to 20 seconds). This will likely result a prolonged period of hazardous seas conditions across the waters. Currently, seas of 15 to 24 feet are forecast from this afternoon through the latter portion of next week. Particularly during next week, the strength and timing of the fronts and resultant sea states are not certain. But, episodes of very steep seas and dangerous bar conditions are expected. -CC/Hermansen && .BEACH HAZARDS...Updated 230 AM PST Friday, December 20, 2024...The unsettled weather will bring increasing swells this week and into the weekend. As additional fronts move through the area, additional swells will build into the waters bringing large breaking waves between 22 to 26 feet to Oregon beaches today into Saturday. Surf lowers only slightly on Sunday, then another system could bring even higher swells causing breaking waves from 25 to 30 feet Sunday night into early next week. A High Surf Advisory has been issued for Saturday morning through Sunday evening to account for the hazardous conditions. Models continue to show this active pattern with increasing surf into early next week. However, the exact details on the magnitude may change as this forecast is refined. Confidence is higher for periods of high surf into this weekend and medium for into early next week. High surf could cause dangerous beach conditions where beach erosion and/or damage to exposed infrastructure will be possible. Stay tuned to the forecast for updates. -CC/Hermansen && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory from 7 PM this evening to 10 AM PST Saturday for ORZ026-030-031. High Surf Advisory from 7 AM Saturday to 10 PM PST Sunday for ORZ021-022. CA...Wind Advisory from 7 PM this evening to 10 AM PST Saturday for CAZ081-085. PACIFIC COASTAL WATERS...Small Craft Advisory until 4 AM PST early this morning for PZZ350-356-370-376. Hazardous Seas Warning until 1 AM PST Saturday for PZZ350-356. Gale Warning from 1 AM to 10 AM PST Saturday for PZZ350-356. Gale Warning until 10 AM PST Saturday for PZZ370-376. && $$ MNF/ANH

038 FXUS66 KEKA 192243 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 243 PM PST Thu Dec 19 2024 .SYNOPSIS...Friday south winds will start to pick up ahead of the next system, but most of the day is expected to remain dry. A strong frontal system is expected to bring a period heavy rain and strong southerly winds to the area Friday night into Saturday morning. Additional atmospheric river storms are expected to arrive in quick succession into next week. && .DISCUSSION...Quiet weather persists across the area this afternoon. Winds have started to turn southerly ahead of the next weather. These remain fairly light in most areas, but have started to increase over the ridges. Tonight these winds pick up as a weak warm front moves over the area and reach 20 to 30 mph over the higher terrain on Friday. Very little or no rain is expected with this warm front. The cold is expected to bring another increase in wind and more rain Friday night and early Saturday. The low levels are expected to be fairly stable and this will keep the winds confined to higher terrain. The soundings are showing 35 to 40 kt winds at 2000 feet and higher in Humboldt and Del Norte counties. This is expected to yield gusts of 45 to 55 mph over the higher terrain with a few gusts to 65 mph near Cape Mendocino. So have added a wind advisory to the interior zones and the King Range. Rainfall amounts with this first system will be moderate with totals ranging from 0.5 inches to over 1.50 inches in the higher terrain. The lowest amounts will be in the valleys of southern Mendocino, southern Lake and eastern Trinity counties. Humboldt Bay is expected to see closer to an inch. The ensemble mean for IVT is briefly showing over 500 kg/m/s so this could bring some high rainfall rates and the totals may end up on the higher end. Saturday morning there is the potential for a thunderstorm or two. Confidence is low on these, but have added them to the forecast. Snow levels are expected to generally be high with this system, it looks like they will be over 6,000 feet for the bulk of the rain. Sunday morning the next system is expected to bring rainfall to the area. The rainfall has trended higher with this system, amounts now look very similar to Saturday`s storm. There will be nearly 24 hours between storms which should allow for the small stream to come down before the next rain. Strong winds are also expected with this storm, once again mainly in the higher terrain of Humboldt and Del Norte counties. The probability of over 35 mph is only around 40 to 60 percent at this point. A break in the rain is expected Sunday night and Monday morning before the next weather system on Monday, but this break may be closer to 12 hours. This is expected to bring 2 to 4 inches of rain from Monday afternoon through Tuesday morning. Stronger winds are expected with system as well. This is the system that may start to bring flooding to the rivers. For more details see the hydrology section. There may be a slightly longer break in the weather Tuesday night and Wednesday. Thursday has the potential for a stronger system that is aimed farther south. This could bring additional flooding to the area if the rivers don`t have time to recede before this next system. The ensembles are showing a 24 to 36 hour gap between these two systems. This ensembles are showing a 50 to 60 percent chance of IVT over 500 kg/m/s for 12 hours with a longer time period over 250 kg/m/s. These probabilities are fairly high considering this is still 7 days away. MKK && .AVIATION...Fog has been the culprit for IFR/LIFR conditions at the coastal TAF sites through mid-morning. Otherwise south light winds and VFR high clouds continued to prevail today. Inland valleys had significant fog which caused a slower progression of improvement and a greater impact on general aviation. For Friday, a mid-high cloud canopy, and solid SSE winds will most likely inhibit significant fog/stratus development at ACV and CEC. However, a Few model guidances do advocate for some measure of IFR/LIFR fog/Cig. There is a possibility for coastal LLWS in the early morning. Interior valleys can expect fog in the morning but maybe not as not as extensive. /TA && .MARINE...The current NW swell in the waters will continue to subside through the rest of the afternoon and into tonight. Tomorrow, an approaching cold front arriving will boost the marine winds sharply before sunrise. Gale force gusts around 45 knots can be expected during the day before increasing even more in the evening with gusts around 50kts in the outer waters and southern inner waters through Saturday early morning. The frontal systems that are forcing the strong winds over the coastal waters is also forecasted to bring multiple pulses of long to mid period swells. The first of these pulses (18ft@15s) is forecasted to arrive Friday afternoon, holding steady through the weekend. A frontal system passing is forecasted to send another pulse (19- 22ft@19s) Monday early morning and a sharp increase in southerly, possibly gale force winds. && .Hydrology...A parade of atmospheric rivers are expected starting Friday night and continuing through late next week. The two over the weekend are relatively weak and focused north of the area. These however will set the stage for a stronger system Monday afternoon through Tuesday morning. Some minor flooding is possible on the Russian by early Tuesday. There is the potential for additional rivers to flood, it will depend a lot on how much the rivers have time to go down between systems. This is especially true for the Eel river due to its size. If the system on Thursday ends up slightly sooner or stronger it could easily cause more significant flooding. MKK .BEACH HAZARDS...A series of long period, westerly swells will continue to impact the coastal waters of Northwest California during next week. The swell this morning was larger than the wave models forecasted, but has subsided through the day and is now more in line with the wave models. GFS Wave model suggest there is another large swell around 16 to 18 feet building across the waters Saturday morning until Sunday morning. This is expected to bring breakers between 20 to 22 feet all day Saturday into the early hours of Sunday. Hazardous surf conditions due to the breaking waves will be possible along west- northwest facing beaches. .EKA WATCHES/WARNINGS/ADVISORIES... CA... Beach Hazards Statement through Friday afternoon for CAZ101- 103-104-109. Wind Advisory from 6 PM Friday to 10 AM PST Saturday for CAZ102-104>106. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 PM PST this afternoon for PZZ450-455-470-475. Gale Warning from 11 PM Friday to 8 AM PST Saturday for PZZ455. Gale Warning from 6 AM Friday to 8 AM PST Saturday for PZZ470. Gale Warning from 6 PM Friday to 8 AM PST Saturday for PZZ475. && $$ Visit us at https://www.weather.gov/eureka Follow us on Facebook and Twitter at: https://www.facebook.com/NWSEureka https://www.twitter.com/NWSEureka For forecast zone information see the forecast zone map online: https://www.weather.gov/images/eka/zonemap.png

116 FXUS66 KMTR 201152 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 352 AM PST Fri Dec 20 2024 ...New AVIATION... .SYNOPSIS... Issued at 234 AM PST Fri Dec 20 2024 A parade of impactful storms will impact the region late tonight through next week. Life-threatening bay, ocean, and beach conditions begin Saturday and linger through next week. && .SHORT TERM... (Today through Sunday) Issued at 234 AM PST Fri Dec 20 2024 Two shortwave troughs will trek across the region over the weekend with the first slated for late Friday night through Saturday and the second slated for Sunday. Both systems will be comparable in terms of rainfall totals with QPF not exceeding 1.50" for either of them and rainfall totals tapering off significantly from north to south. Southerly winds will increase as the shortwave troughs move across the area, but they will remain below Wind Advisory criteria. While these two systems are not looking to be overly impactful in and of themselves, they will be responsible for the antecedent conditions going into the more impactful systems next week. As soils approach saturation it is more likely that trees will fall, mud and rock will slide, and creeks and streams will rise. SPC has highlighted most of Marin and Sonoma Counties for general or non-severe thunderstorms between 4 AM Saturday and 4 AM Sunday. A High Surf Advisory will go into effect at 6 AM Saturday and run through 4 PM Sunday with life-threatening bay, ocean, and beach conditions lingering into next week. If you want to see large breaking waves, there`s an app for that (Surfline), do not go to the beach. && .LONG TERM... (Monday through Thursday) Issued at 234 AM PST Fri Dec 20 2024 Monday through Thursday will be the most critical time period as two more shortwave troughs plow through the region, the first slated for Monday morning through Tuesday morning and the second slated for Wednesday afternoon through Thursday. Both of these systems will bring widespread impactful rainfall with rainfall totals as high as 2.50" with the Monday-Tuesday system and up to 3.50" with the Wednesday-Friday system. WPC has highlighted Marin, Napa, and Sonoma Counties for a marginal or at least 5% risk of rainfall exceeding flash flood guidance between 4 AM Monday and 4 AM Tuesday. As the rivers rise so do flooding concerns with deterministic forecasts showing a rapid rise beginning Monday night. The greatest chance for convection is with the Monday morning-Tuesday morning system with chances for thunderstorms up to 20%. There is up to a 30% chance in reaching Wind Advisory criteria (wind gusts 45+ mph) with these systems. Life-threatening bay, ocean, and beach conditions will return Monday and continue through next week with a High Surf Warning likely needed during this time frame. Below are mainstem forecast points and the ensemble forecast of exceeding (action/monitor stage), (minor flood stage) between Monday and next Sunday. Sonoma County: Russian River - Guerneville (GUEC1): 39%, 34% Russian River - Healdsburg (HEAC1): 11%, N/A Napa County: Napa River - St. Helena (SHEC1): 43%, 20% Napa River - Napa (APCC1): 30%, 11% Santa Clara County: Guadalupe River - San Jose at Almaden Expressway (GUDC1): <2%, <2% Santa Cruz County: San Lorenzo River - Big Trees (BTEC1): 5%, N/A Monterey County: Carmel River - Robles Del Rio (RDRC1): <2%, <2% && .AVIATION... (12Z TAFS) Issued at 350 AM PST Fri Dec 20 2024 Satellite imagery showing high clouds streaming over the region with low level clouds over the North Bay and East Bay (generally IFR/LIFR). This is expected to continue through mid-morning before conditions improve after around 18Z. Winds stay light to moderate through the TAF period. As the next rain system approaches, winds aloft increase leading to LLWS concerns tonight into Saturday morning, with light rain to follow over the Bay Area terminals. There is also moderate confidence of lowering ceilings over the southern terminals by late this evening and into Saturday morning. Vicinity of SFO...VFR conditions expected through most of the day with lowering ceilings late this evening and more so into Saturday morning. Southerly winds increase tomorrow morning as a cold front approaches the region. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR conditions expected with southerly winds this morning becoming variable by mid-morning. This evening the potential increases to see lowering ceilings between 700-1500 ft. && .MARINE... (Today through Wednesday) Issued at 234 AM PST Fri Dec 20 2024 Dry weather continues through Friday before an active weather pattern develops across the Pacific bringing rain and gusty winds this weekend and again early next week. Gale force gusts could be possible across the northern waters on Saturday. Wave heights will remain elevated through late next week with 15 to 20 feet waves Monday through Wednesday. Persistent dangerous conditions for small crafts are expected Friday into next week. && .BEACHES... Issued at 350 AM PST Fri Dec 20 2024 Elevated surf of 15 to 18 feet, with occasional breakers up to 20 feet, will occur Saturday morning to Sunday afternoon as another system approaches the West Coast, with a High Surf Advisory issued for the Pacific coast from 6 AM Saturday through 4 PM Sunday. Then, a very large and powerful, long period west swell train will likely arrive along our entire coastline Monday into Tuesday next week. Current global wave models are forecasting swell heights to 20+ feet with very energetic swell periods of 20+ seconds, this will lead to much higher breakers including localized coastal flooding impacts. Stay tuned for further updates. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...High Surf Advisory from 6 AM Saturday to 4 PM PST Sunday for CAZ006-505-509-529-530. PZ...Small Craft Advisory from 9 AM this morning to 3 PM PST Saturday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 9 PM this evening to 3 PM PST Saturday for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10- 60 NM-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 3 PM this afternoon to 3 PM PST Saturday for Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Sarment LONG TERM....Sarment AVIATION...RGass MARINE...RGass Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea

873 FXUS66 KOTX 201153 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 353 AM PST Fri Dec 20 2024 .SYNOPSIS... A ridge of high pressure will result in a drying trend and calmer winds through Friday with a return of areas of stratus and fog. Unsettled weather will return this weekend and continue into next week. Mild temperatures will result in precipitation falling primarily as valley rain and mountain snow. Check mountain pass forecasts and conditions often before traveling. && .DISCUSSION... Today through Sunday: Ridging to our east will keep us in an active southwesterly flow regime with three distinct shortwaves on track to ripple through the Inland Northwest by the end of the weekend. The first of the three waves will be the weakest and will pass through during the day today. This wave will bring wintry precipitation to the Cascade crest while the rest of the region stays dry. Our second wave will move in tomorrow and will bring more widespread precipitation. For the Cascade crest and northern mountains precipitation will be in the form of snow, and for valleys just east of the Cascades and more sheltered northern valleys where cold air has a harder time mixing away from the surface, periods of freezing rain will be possible. Lowlands/valleys elsewhere will see rain. The third wave will arrive late Sunday morning and will bring precipitation overnight into Monday. Heavier snow in the Cascades is expected with this wave, with 6 to 9 inches in the forecast for Stevens Pass. Freezing rain will once again be possible for the Cascade valleys and northern valleys with accumulations up to 0.15 inches possible. Daytime highs will be in the 30s to low 40s, and lows will be in the 20s to low 30s. /Fewkes Monday and Tuesday: The period starts under weekend trough continuing to bring mountain snow and valley rain to the region. The activity will slowly taper off through the morning. Monday afternoon is expected to be relatively quiet. The next round of precip is expected arrive early Tuesday morning. It will bring another round of widespread mountain snow and valley rain to the region. Snow amounts for the will be highest in the Cascades with Stevens Pass receiving 4 to 8 inches. Highs will continue to balmy with the Southern flow pattern. The range will be in 30s to mid 40s. Overnight lows will be in the upper 20s and 30s. Wednesday through Friday: Wednesday will start relatively calm as a brief shortwave ridge builds in behind the exiting system. It will be short lived as ensembles bring a more robust colder wave across the Pacific Northwest. With the colder air mass, mountain snow will continue with Stevens Pass having a 70% probability of 6 inches and 20% of one foot. Rest of the mountain areas range from 4 to 8 inches. The colder air can bring snow to the valleys and northern portion of the Basin. The probability of an inch range from 60 to 80 percent for Wednesday night into Thursday morning. Spokane is around 20 percent for one inch of snow. By Friday, the region will be under a zonal flow pattern with several waves of moisture. While it is expected to continue to be mountain snow, there is low confidence on the precip type for the lower elevations. Temperatures in the area lean more toward rain and wintry mix. Highs will be in the 30s. Overnight lows will be in the upper 20s and 30s. /JDC && .AVIATION... 12Z TAFS: Patchy fog and low ceilings have returned in the valleys of northern WA and the ID panhandle as well as around KMWH. Satellite imagery is showing fog attempting to creep into the GEG/COE area, so development of IFR ceilings and reduced visibilities will be possible for those sites through the morning. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence for IFR conditions persisting at MWH through 14Z. Low confidence on if/when IFR conditions will develop at GEG/COE. ----------------------- Confidence descriptors: Low - Less than a 30 percent chance Moderate - 30 to 70 percent chance High - Greater than a 70 percent chance For additional probabilistic information for NWS Spokane airports, please refer to the Aviation Dashboard on our webpage: https:/www.weather.gov/otx/avndashboard && .PRELIMINARY POINT TEMPS/POPS... Spokane 42 31 43 33 43 36 / 10 0 70 80 0 90 Coeur d`Alene 45 32 43 34 42 36 / 10 10 60 90 0 90 Pullman 46 35 45 31 42 36 / 10 0 60 80 0 100 Lewiston 51 38 47 36 47 39 / 0 0 40 50 0 90 Colville 40 29 39 31 38 33 / 10 10 70 80 20 100 Sandpoint 42 33 40 32 42 30 / 10 10 50 100 10 90 Kellogg 46 36 48 36 43 37 / 10 10 60 100 10 90 Moses Lake 43 31 40 32 43 34 / 10 0 90 20 30 80 Wenatchee 41 34 40 33 38 33 / 10 0 90 10 50 90 Omak 40 37 41 32 41 32 / 10 0 80 30 30 90 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$

589 FXUS66 KPDT 201137 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 337 AM PST Fri Dec 20 2024 .Updated Aviation Discussion. .SHORT TERM...Today through Sunday night...A progressive flow pattern will be observed during the short term period, but each wave that travels across the forecast area is relatively weak and not a significant precipitation producer. Water vapor loops show a fast moving shortwave exiting the forecast area and currently along the ID border. The system brought little in the way of precipitation...less than 0.1" of rain for most locations. It has provided some mixing of the stratus, and the fog has lifted over most of the Blue Mtn Foothills where a Dense Fog Advisory is currently in effect. I`ll wait just a little longer to see if fog will return. If not, the advisory will be cancelled. A couple more embedded waves in the southwest flow aloft will bring light showers (snow above 6K feet) later this morning and afternoon to the WA Cascades but only mid and high level clouds elsewhere. The shortwave trough on Saturday will be a little stronger, arriving as a negative tilt wave Saturday afternoon. The GFS and ECMWF show a 300-400 IVT east of the Cascades, indicating areawide precipitation but not a strong AR. PoPs will be 80-100% across the board Saturday afternoon. Thoughts remain the same that the mountains will likely receive 0.25-0.5" of liquid precipitation while the lower elevations will receive a few hundredths to 0.25". Cold air advection aloft will lower snow levels down to around 4000-4500 feet, but the modest QPF keeps the confidence high that no winter highlights will be needed. The NBM continues to show patchy light freezing rain late tonight and early Saturday along the east slopes of the WA/OR Cascades, but the latest HREF shows little to none. Since overnight lows will be in the lower 30s for the mountain passes such as Snoqualmie, White Pass and Santiam, the probability for ice accumulations on I-90 or the main highways is very low. Although no winter highlights are planned, a wind advisory will be issued for the Grande Ronde Valley for late tonight through Saturday. Surface gradients as strong as 9 mb will set up between ONO-MEH, leading high confidence that sustained winds around 30 mph gusting to 45-50 mph will be met. Localized winds of the same magnitude are likely (60% chance) near the wind prone area along Cabbage Hill, but will hold off on an advisory for the Blue Mtn Foothills due to lower confidence of anything more than isolated strong winds early Saturday morning. The next shortwave is progged to arrive late Sunday and Sunday night, taking a similar track and with similar QPF potential. This system will bring better potential for snow accumulations due to the snow levels starting at 3500-5000 feet rising to 4000-6000 feet overnight. Due to increasing snow levels, most of the mountain passes will have light amounts of snow. It is the higher elevations of the WA/OR Cascade east slopes that have probabilities of 5-8" of new snow (40% chance). It will once again be windy in the Grande Ronde Valley. Wister/85 .LONG TERM...Monday through Friday... Key Messages: 1. Widespread rain and mountain snow Monday into Tuesday. 2. Breezy winds Monday evening through Tuesday morning. 3. Widespread precipitation and breezy winds return Wednesday night. The extended period is characterized by a rather active pattern as several upper level shortwaves are expected to pass across the area through the week. Luckily, southwest flow aloft will attribute to elevated snow levels that will keep mountain snow confined to elevations above 6000 feet early in the week. This is primarily associated with the first shortwave, which will approach the area on Monday before passing just to our south Tuesday afternoon. As a result, rain chances will increase west to east through Monday afternoon before chances peak (70-95%) overnight into Tuesday morning. Rain looks to taper off across lower elevations of the Columbia Basin and Central Oregon Tuesday afternoon and evening as a weak transient ridge follows closely behind the exiting trough and attendant frontal system. Rain amounts on Monday look to stay focused across our western zones as 0.10-0.30" is expected along the east slopes of the Cascades, Central Oregon, the Gorge, and the Yakima/Kittitas Valleys, with only 0.05-0.15" expected along the Blue Mountain foothills and lower elevations of the Columbia Basin. Confidence in these rain amounts is moderate (50-70%) as the NBM suggests a 30-80% chance of 0.15" or more over the east slopes, Central Oregon, the Gorge, and the Yakima/Kittitas Valleys, and a 35- 75% chance of 0.10" or greater across lower elevations of the Columbia Basin and the foothills of the northern Blue Mountains. The large range in rain amount probabilities coupled with moderate confidence in current amounts is related to differences in guidance in relation to the strength and timing of the incoming shortwave. 52% of ensemble clusters hint at a slightly wetter outcome than the current forecast, which relates to a stronger and deeper trough. The other 48% of ensembles are wetter on Tuesday as they relate to a slower arrival of the trough and attendant frontal system. Tuesday does look to be the wetter of the two days as 0.20-0.40" of rain is expected across lower elevations of the Columbia Basin and the northern Blue Mountain foothills. Confidence in these rain amounts is still moderate (50-70%) as the NBM showcases a 45-75% chance of 0.25" of rain or more over the Basin and Blue Mountain foothills. This early week system will also bring mountain snow across the Cascade and Blue Mountains, with the majority of accumulations occurring at elevations of 4500 feet and above. Accumulations of 2-5 inches is likely above 4500 feet, with 1-2 inches possible across our Cascade Passes. Confidence in these snow amounts are high (80%) as the NBM suggests a 50-75% chance of 1 inch or more for both Santiam and White Pass. The frontal system associated with the early workweek system will also allow a pressure gradient to develop along the Blue Mountains. This will lead to breezy winds across the Grande Ronde Valley and the foothills of the Blue Mountains as gusts of up to 40 mph will be possible, peaking over the early morning hours on Tuesday. The strongest pressure gradient and highest winds are likely to set up across the Grande Ronde Valley as the GFS highlights a 5 mb pressure gradient between Baker City (KBKE) and Meacham (KMEH), which does meet the normal advisory threshold of 5 mb. However, an advisory is not currently expected as the NBM highlights a 50-70% chance of gusts reaching 40 mph or greater and a 25-45% chance of gusts reaching advisory levels (45 mph or greater). Another transient upper level ridge follows closely behind the departing system late Tuesday into Wednesday, which will bring a brief respite in widespread precipitation. This will not last long as another upper level trough will approach the region late Wednesday into Thursday. Guidance and ensemble members are suggesting that the incoming trough will be negatively-tilted, which would allow colder air to infiltrate into lower elevations of the Basin more effectively to drop snow levels to between 3500-4500 feet north-to-south. These lower snow levels will lead to accumulations of 2-8 inches on Wednesday and 5-8 inches Thursday across our Cascade Passes. 7-12 inches of snowfall is likely above 4500 feet across the Cascades and northern Blue Mountains. These amounts over our Cascade Passes would be enough to warrant a Winter Weather Advisory, but current confidence in these snow amounts is moderate (40-50%) as the NBM suggests a 40-60% chance of 6 inches of snow or more over Santiam and White Passes on Thursday. Widespread rainfall is also anticipated across lower elevations below 4000 feet as 0.15- 0.30" is currently forecast across lower elevations of the Columbia Basin and the northern Blue Mountain foothills. Winds also look to be breezy across the Grande Ronde Valley and the northern Blue Mountain foothills as the GFS suggests that another pressure of 5-6 mb will develop along the northern Blue Mountains to allow gusts of up to 40 mph to occur. Confidence is moderate to high (60-80%) in these wind values as the NBM advertises a 55-80% chance of 40 mph gusts or greater over the Grande Ronde Valley and the northern Blue Mountain foothills. Confidence is moderate (60-70%) in the issuance of a wind advisory late Wednesday into Thursday morning across the Grande Ronde Valley as the NBM suggests a 55-70% chance is gusts reaching advisory-level winds (45 mph or greater). 75 && .AVIATION...12Z TAFS...VFR conditions currently at most sites, with KDLS (MVFR) and KPDT (LIFR) being the exceptions due to reduced visibility of 4SM at KDLS and 3/4SM at KPDT. These conditions are expected to persist through much of the morning and include KALW as surface high pressure has allowed cold air to be trapped in isolated areas around these terminals, developing pockets of dense fog in these areas. Elsewhere, low winds (5kts or less) are anticipated as flight categories stay VFR through the period. 75 && .PRELIMINARY POINT TEMPS/POPS... PDT 43 33 43 33 / 0 0 80 30 ALW 43 34 45 36 / 10 0 80 50 PSC 43 34 41 36 / 0 0 80 20 YKM 43 30 40 30 / 10 0 90 10 HRI 43 33 41 34 / 0 0 90 20 ELN 43 33 41 30 / 10 0 90 10 RDM 50 35 47 30 / 10 0 80 0 LGD 46 36 44 31 / 0 0 80 50 GCD 49 34 46 30 / 0 0 90 20 DLS 46 38 43 36 / 10 10 100 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory from midnight tonight to 3 PM PST Saturday for ORZ049. WA...None. && $$ SHORT TERM...85 LONG TERM....75 AVIATION...75

902 FXUS65 KREV 201101 AFDREV Area Forecast Discussion National Weather Service Reno NV 301 AM PST Fri Dec 20 2024 .SYNOPSIS... * Valley inversions and areas of freezing fog linger through this morning. Otherwise, dry and mild weather prevails today. * A quick-moving storm will bring strong gusty winds, light rain showers, and high elevation snow showers this weekend. * A stronger storm remains possible on Christmas Eve, likely impacting holiday travel. && .DISCUSSION... Today will be the final day in a series that features dry, quiescent conditions before we enter a stretch of much more stormy, unsettled weather to wrap up 2024. Residual inversions will likely yield another morning of low stratus and freezing fog for the Honey Lake Basin, Smoke Creek/Black Rock deserts, the Martis Valley, and the Tahoe Basin before mixing out this afternoon. Otherwise, expect mild daytime highs in the upper 40s and 50s. Our incipient storm arrives on Saturday, providing light rain, high elevation snow, and strong gusty winds. The latter appears to be the most impactful as southwest/west winds approach 35-45 mph across lower elevation Sierra communities and the Sierra Front Saturday morning/afternoon with wind gusts exceeding 90 mph along exposed Sierra ridgetops. Be prepared for impacts to recreation and bumpy flights into and out of regional airports. Rain and snow totals will be meager with this storm with accumulating snowfall of only 1-4" confined to elevations above 7000-7500 feet by Sunday night. Still, there may be some slick roads and travel delays for Sierra passes this weekend. Elsewhere, light rain of a few hundredths to perhaps a couple tenths is expected over the weekend. We`re still on track for a stronger storm Monday night and Tuesday (Christmas Eve), bringing another bout of gusty to strong winds and heavier mountain snowfall compared to its predecessors. However, rain and snow amounts have trended downward quite considerably in latest guidance. There is still high confidence that this storm will provide heavy snow to Sierra passes, which will likely result in travel delays leading up to Christmas. Additionally, gusty winds will yield more turbulent flights Tuesday. There is still much to be determined with this storm as guidance wavers, but the key takeaway is this: Do your holiday travel on Monday, and be prepared for slick roads and slowdowns in/across the Sierra if you must travel on Christmas Eve. On a brighter note, there`s a good chance (>40%) that most Sierra residents wake up to a White Christmas. Those of you in the Greater Reno-Carson-Minden area, well, you`ll just have to keep dreaming. -Salas && .AVIATION... The main weather impact today will be IFR/LIFR conditions at KTRK/KTVL until around 18z due to FZFG. KRNO/KCXP/KMEV may see reduced slantwise visibilities due to hazy skies through this morning. Otherwise, VFR conditions will prevail today. An approaching storm will bring periods of LLWS and turbulence late tonight and Saturday with rain and snow showers to regional terminals over the weekend. Biggest impacts will be from the wind Saturday as latest CAMS show a potential critical layer developing near the Tahoe Basin and along the Hwy 395 corridor. There is a 2-4 hour window where gusts could approach or exceed 40 kts (70% chance) between 16Z-22Z in these areas. -Salas && .REV Watches/Warnings/Advisories... NV...None. CA...None. && $$

363 FXUS66 KSTO 201019 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 219 AM PST Fri Dec 20 2024 .SYNOPSIS... Dry weather with morning fog expected today First storm in a series of systems will move into area Saturday followed by more systems into mid week next week including Christmas. .DISCUSSION... Areas of dense fog have developed around the Sacramento Valley once again this morning. Lowest visibilities are being observed in the northern Sacramento Valley, with Redding AP at 1/4 mile and Red Bluff AP at 1/2 mile. Low visibilities due to fog are expected to continue this morning, and a Dense Fog Advisory is in effect for the Sacramento and northern San Joaquin Valley until 11 AM this morning. If you encounter areas of dense fog on the morning commute, slow down, leave plenty of space between you and the car in front of you, and use your low-beam headlights. Outside of the morning fog, today will be the last dry and quiet weather day for the area, as a series of storms is expected to move into the area beginning tomorrow morning. An area of low pressure in the PacNW will eject a relatively warm trough with precipitation chances across the area. The better moisture with this system still looks to remain mostly north of our area, however the northern Sacramento Valley, southern Cascades, and the Sierra and adjacent foothills will see the heaviest of precipitation. Latest rain totals from this first wave have remained unchanged from yesterday`s forecast. Aforementioned locations stand to receive around 0.75 to 1.25 inches of rainfall through early Sunday morning. Snow levels continue to remain above 6000 feet for the Sierra, and around 5500 feet for the mountains of NW Shasta County. Total snow accumulations look to remain around a dusting to 2 inches, with locally higher amounts on peaks and specifically at Lassen NF/NP. Late Saturday night into early Sunday morning, a brief break from widespread rain/showers and high elevation snow is expected. Another wave of precipitation then enters the area Sunday morning, with similar impacts and snow levels above 8000 feet, as warm southerly air continues to flow into the area. NBM probabilities remain at around 15-30% for locations in the central/southern Sacramento Valley, Delta, and northern San Joaquin Valleys, while a 65-90% chance for 0.50 inches in the northern Sacramento Valley, mountains and foothills through Monday morning. Overall, mountain travel this weekend does not look to be majorly impacted, with primarily wet roads as the potential travel concern. Another brief reprieve from widespread precipitation is expected Monday afternoon, then a third, wetter, and cooler system is expected to move in. The third system is expected to bring precipitation chances Monday afternoon through early Christmas Day. Of the three systems in the short term forecast window, this system will have better moisture support for the entire region. While the higher precipitation totals will still be in the northern Sacramento Valley, mountains of Shasta County, southern Cascades, Lassen NF/NP, and the Sierra and adjacent foothills. NBM probabilities of at least an inch of rainfall through early Christmas morning are around 70-100% for the above mentioned areas, while the rest of the Valley, mainly from Redding southward 40-70% chance of an inch. Cooler air is anticipated to rush in behind this system, so snow levels will fall as the main wave makes landfall and pushes inland. Snow levels begin at around 8000 feet Monday night/Tuesday morning, then fall to around 5000-6000 feet Tuesday night. While the bulk of the precipitation will have moved out of the area as the coldest air arrives, accumulations of snow could impact Christmas Eve travel during the nighttime at around 6000 feet and higher. NBM probabilities of around 6 inches of snow at elevations 6000 feet and higher are around 30-50%, so we are not anticipating major impacts to travel at this time, however an Advisory may be needed to cover higher snowfall rates and accumulations. Breezy southerly winds will also accompany this third system, with strongest winds in the Valley from Yuba City to Redding and in the mountains and foothills of the Sierra. If you have travel plans this weekend through Christmas, please check road conditions before heading out, and keep checking the forecast for changes. .EXTENDED DISCUSSION (Tuesday THROUGH Friday)... As mentioned in the short-term forecast discussion, the third system will continue into early Christmas Day, then another break in precipitation is likely until later Christmas night. Ensembles depict another trough ejecting into the area, slightly further south and eastward than previous troughs. With the current EC ensemble guidance track, this system will be cooler and could bring widespread precipitation to the region all day Thursday and into Friday morning. Early forecast precipitation totals may be running too hot, as probabilities of snow in the mountains are around 30-60% for 6 inches of snow at around 5500-6000 feet and higher, but the totals forecast are around 6-13 inches. Heavier rain totals look to once again be in the northern Sacramento Valley, southern Cascades, Lassen NF/NP, and the Sierra and adjacent foothills, but again the probabilities the NBM are showing are skewed from the forecast rain totals. There is much uncertainty with this system, as clusters have to resolve a definitive solution to track and strength. Stay tuned to the forecast for updates as we move through the weekend when ensembles and cluster analysis come into better agreement. && .AVIATION... MVFR/IFR with LIFR conditions in BR/FG and/or low ceilings expected through 20Z-22Z Friday in the Valley. BR/FG may lift into a low stratus deck beyond 20Z-22Z Friday. Surface winds generally below 12 knots next 24 hours, then increasing southerly winds after 12Z Saturday. Local gusts up to 20 kts in the foothills/Sierra through 18Z Friday. MVFR / local IFR conditions after 06Z Saturday as Pacific weather system moves through interior NorCal. && .STO WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 11 AM PST this morning for Carquinez Strait and Delta-Central Sacramento Valley-Northern Sacramento Valley-Northern San Joaquin Valley-Southern Sacramento Valley. && $$

509 FXUS65 KMSO 200839 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 139 AM MST Fri Dec 20 2024 .DISCUSSION... KEY MESSAGES: - High pressure will persist through Saturday - The next chance for precipitation will be Saturday night with a potential for freezing rain on Sunday morning Satellite imagery early this morning shows a fast-moving shortwave disturbance exiting the Northern Rockies to the east. High pressure will resume today and persist through Saturday. There will be enough moisture associated with the ridge to keep intermittent cloud cover in the forecast. A more significant trough of low pressure remains on track to move through north-central Idaho and western Montana Saturday night into Sunday. Pre-frontal warming will raise snow levels, leading to a wintry mix in the valleys and the potential for freezing rain, depending on the thermal profile. The GFS model shows a faster cold front with valley snow Sunday morning, while the ECMWF model suggests slower timing and higher snow levels. The timing of the cold front will determine the extent of freezing rain. Next week, ensemble guidance indicates an active weather pattern with fluctuating snow levels. Expect continued wintry mix in valleys and accumulating snow at mountain passes and higher elevations. && .AVIATION...Light and variable winds under overcast skies will persist today under a ridge of high pressure. Some low stratus down to about 4000 ft AGL will be possible today at KGPI with a stable atmosphere. Expect decreasing clouds overnight tonight with continued light and variable winds. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$

996 FXUS65 KBOI 201026 AFDBOI Area Forecast Discussion National Weather Service Boise ID 326 AM MST Fri Dec 20 2024 .SHORT TERM...Today through Sunday night...Inversion and areas of fog are in the valleys under high pressure aloft. But the current Dense Fog Advisory looks dubious and we may cancel it before its 11 AM MST expiration time. The Treasure Valley has not been as cold in this inversion as it was in the previous one, but the Camas Prairie has become much colder this time with yesterday`s high temp at Fairfield barely above 20 and current temp near zero. A weakening Pacific trough will bring clouds but no pcpn to our CWA on Saturday. A stronger Pacific trough will bring light pcpn to northern areas Saturday and mixing winds to southern areas, possibly strong enough to scour the`inversion. After brief clearing Sunday morning a wetter Pacific system will come inland with widespread valley rain and mountain snow and further low-level mixing. A cold front will follow late Sunday night with more pcpn. .LONG TERM...Monday through Friday...An active pattern is expected during the extended period. A break in precipitation will arrive on Monday as an upper level trough moves east and a ridge of high pressure moves inland. The break will be short-lived as another Pacific trough moves inland on Tuesday. This will bring a 70-90% chance of rain and snow to the area, with moderate precipitation amounts expected. Southwest flow aloft ahead of the system will bring mild air into our region, pushing snow levels up to 5000-7000 feet. However, much of the precipitation is expected along the cold front, with snow levels falling to 3500-5500 feet. Precipitation should be mostly rain in the lower valleys, with several inches of snow possible in the mountains. High temperatures Monday and Tuesday will average around 10 degrees above normal with breezy winds on Tuesday as the front moves through the area. Drier, cooler, and breezy conditions are expected Christmas Day as the trough moves east. However, a deep upper low in the Gulf of Alaska will bring abundant moisture and a series of shortwave troughs (possibly an atmospheric river event) into the Pacific Northwest Thursday and Friday, likely continuing into the following weekend. Moderate to heavy precipitation totals are expected from this pattern, with a continuous 60-90% chance of precipitation Thursday through Friday, which is high this far in advance, and is a long duration to maintain high PoPs. This system will be cooler than the system earlier in the week, but not quite cold enough to favor significant valley snow, as snow levels are projected to be 3000-4500 feet. However, heavy mountain snow will certainly be possible late next week into the following weekend. Temperatures are forecast to average around 5 degrees above normal with breezy winds Thursday and Friday. && .AVIATION...Patchy LIFR fog in lower valleys this morning, including near KBNO, KBKE, KONO, KEUL, and KMYL. However, high clouds may prevent fog from becoming widespread. Surface winds: variable less than 10 kt, except easterly 10-20 kt near KJER/KMUO. Winds aloft at 10kft MSL: W-SW 15-25 kt. KBOI...Generally VFR. High clouds expected to prevent fog formation near the terminal. Surface winds light and variable. Weekend Outlook...Light valley rain and mountain snow will move west to east late Saturday. A brief break in precipitation is expected late Saturday night into Sunday morning before more rain and snow arrive late Sunday. MVFR to LIFR in precipitation with snow levels generally 4000-6000 ft MSL. Mountains obscured. Surface winds: generally SW-SE 5-15 kt each day, with gusts 25-35 kt across portions of SE Oregon. Low level wind shear possible Saturday. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Dense Fog Advisory until 11 AM MST this morning IDZ011-012-033. OR...Dense Fog Advisory until 11 AM MST /10 AM PST/ this morning ORZ061-063-064. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise SHORT TERM...LC LONG TERM....ST AVIATION.....ST

122 FXUS65 KLKN 200810 AFDLKN Area Forecast Discussion National Weather Service Elko NV 1210 AM PST Fri Dec 20 2024 .SYNOPSIS...Fair weather on Friday beginning to transition to a more active pattern on Saturday. Best chances for active weather and widespread accumulating precipitation will be Sunday and Christmas eve into Christmas. && .SHORT TERM... Upper level ridging continues on Friday into Saturday before a trough passing to the north begins to break that ridge and allow a more active pattern in the long term. Returning to the short term, ridging continues to allow temperatures to soar on both Friday and Saturday, with all areas 10-15 degrees warmer than normal and Elko, Tonopah, and Ely currently forecast to approach or break record high temperatures one or both days. Friday remains quiet across the area, with light winds (less than 10 mph) and no significant weather. Winds pick up slightly on Saturday with the trough passage, but still look to remain below 15 mph. Some precipitation is possible in Elko and Humboldt counties but no measurable accumulation is expected on Saturday outside of mountain peaks. Mountain passes have less than a 5% chance of seeing a trace of precipitation before midnight on Saturday and valley locations have less than a 1% chance. .LONG TERM...Sunday through next Thursday A consistent on-and-off weather pattern expected throughout the long term. Sunday will start off with active weather as the low pressure system from Saturday remains over the state with a 50-90% chances northern Nevada could see up to 0.05 to 0.1 inches of rain, while central Nevada remains dryer with a 10-30% chance of 0.01-0.02 inches along the US-50 corridor while south of US-50 remains dry. The warmer than normal temperatures is expected to keep snow levels above 7000 feet, keeping snow accumulations more over the mountains up to 1 inch. High temperatures expected to be in the 40s in northern Nevada while central Nevada in the mid 40s to 50s. Overnight lows also expected above normal with temperatures in the high 20s to mid 30s. Breezy southwesterly winds in the higher terrains along the northern border with Idaho, light winds everywhere else. Monday, a break in the weather as the low pressure trough weakens Sunday night with an upper level ridge builds back up. Temperatures will be slightly warmer in the 40s to 50s across the region with light winds during the day. By the evening, cloud cover begins back up with some breezy southerly winds at 10-15 mph as the ridge weakens with another low pressure system moving in from the northwest. Overnight lows remain in the 20s to 30s. Tuesday, the low pressure system moves over the silver state in the early overnight hours, bringing in a cold front with more chances of precipitation with chances up to 40-60% of seeing up to 0.1-0.2 inches of rain in central Nevada (0.02-0.07 in N. Nye County) and a 60-90% of seeing up to 0.1-0.25 inches of rain in northern Nevada (western Elko county up to 0.02 inches). Snow levels drop to below 5000 feet in the late afternoon to evening hours transitioning rain to snow as cooler air moves in from behind the front, however by that time, the weather is expected to dissipate around the same time with a 35-55% chance for eastern Nevada late in the evening. Snow accumulations in valleys could see up to 0.1-0.2, with higher elevations and passes seeing up to 0.5 inches, while mountains could see up to 2-5 inches (up to 8 inches along Ruby Mountains). Overnight lows expected to be cooler from the cold front with lows in the low to mid 20s. Breezy southerly winds to start the day at 10-15 mph and transitioning to a more westerly direction by the afternoon. Christmas day, another brief lull in the weather early morning as the low pressure system pushes east and a weak upper level ridge moves in, however by the afternoon to evening hours, the break in weather ends as another low pressure system from the northwest moves back over the state. High temperatures expected to be cooler yet remain above normal in the mid 30s to low 40s along with light winds. By the afternoon to evening hours, the next system moves in over northern Nevada bringing in more chances of precipitation, with a 50-65% chance of seeing some trace amounts of snow as overnight lows expected to be in the low 20s. Winds begin to elevate from the passing front along the northern border at 15-20 mph. Thursday, the system pushes further south reaching into central Nevada along the US-50 corridor. A 30-45% chance of precipitation along the US-50 corridor and extending south across the northern half of N. Nye County, however Tonopah expected to be drier with only a 10% chance. Northern Nevada along I-80 and north of the corridor seeing a 50-75% chance of precipitation. Snow levels rise to just above 5000-6000 feet during the day then lower to 4600-5500 feet overnight, allowing snow to reach the valleys. Snow accumulations in the valleys expected to be up to 0.1-0.3 inches (up to 0.5 in Ely) with higher elevations and passes seeing up to 1-1.5 inches, with mountains receiving mainly snow up to 5-8 inches. High temperatures remain in the 40s with overnight lows reaching down into the mid 20s. Breezy southwesterly winds along the higher elevations and mountains at 10-15 mph, with lighter winds in the valleys. && .AVIATION...Look for VFR conditions and light winds through the next 24 hour period. && .LKN Watches/Warnings/Advisories... None. && $$ 94/97/86