564 FXUS66 KSEW 210326 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 826 PM PDT Wed Aug 20 2025 .SYNOPSIS...High pressure builds into the Pacific Northwest starting Thursday for a warming and drying trend that will continue through the weekend. Areas of widespread Moderate HeatRisk will persist over the weekend and into early next week. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...High pressure will build into the Pacific Northwest on Thursday and will amplify across the region heading into the weekend. Highs will climb a few degrees on Thursday, topping out in the upper 70s to low 80s across the interior and in the low to mid 70s for the coast. Further warming and drying is expected on Friday and Saturday as a thermal trough at the surface creeps northward into western Washington and periods of offshore flow develop. Afternoon highs will be in the upper 70s to low 80s along the coast and in the 80s to low 90s across the interior. Overnight lows will be warmer each morning, bottoming out in the upper 50s to low 60s by Saturday. Little relief will be felt during the overnight hours, especially for urban areas, by Saturday. With hot daytime temperatures and warm overnight lows, widespread Moderate (Orange) HeatRisk will persist across the region. In addition to the heat, elevated fire weather conditions will due the warming and drying trend with minimum humidities dipping down into the 20s and teens in spots across the Cascades and south Sound. For more info, see the fire weather section below. .LONG TERM /SUNDAY THROUGH WEDNESDAY/...Warm and dry conditions will continue through the weekend, with temperatures on Sunday looking similar to Saturday for another day of widespread Moderate HeatRisk across the region. Ensembles are in slightly more agreement with the ridge of high pressure remaining over the area into early next week for continued above average temperatures. Onshore flow will return to cool areas along the coast, but does not look strong enough to cool areas across the interior at this time. Thus, Moderate HeatRisk will prevail across the interior areas, especially east of the Sound, on Monday and Tuesday. Temperatures may moderate some by Wednesday, but generally still look to remain roughly 5 to 10 degrees above normal at this time. 14 && .AVIATION...Generally zonal flow over W WA tonight and into Thursday as upper level ridging starts to build into the area. Surface winds mostly northerly in nature, however some variances to the NW or NE are being observed, with speeds ranging 5-10 kts. Exceptions directionally include BLI with southerly winds and CLM with westerlies. Widespread VFR conditions this evening and expected to continue for most terminals for the TAF period. Locations more prone to lower cigs could see some FEW-SCT low clouds but any cigs will likely be reserved for along the coast with a period of IFR conditions expected in the early morning hours. Any low clouds expected to burn off quickly, with VFR at all terminals expected to resume by late Thursday morning. KSEA...VFR conditions in place and will persist for the TAF period. Northerly winds this evening at 8 to 12 kt will ease to 6 to 10 kt overnight before regaining speed by 18Z. Wind direction may wobble slightly, northwesterly being favored this evening and Thursday afternoon while northeasterly may be preferred overnight tonight and Thursday night. 18 && .MARINE...An upper level ridge will slowly move inland over the next couple of days, resulting in the development of a thermal trough along the coast by this weekend. A weaker marine push through the Strait this evening should keep winds below SCA criteria, although an occasional gust around the lower end of this threshold cannot be completely ruled out. Once the thermal trough moves inland on Sunday, breezy north winds in the outer coastal waters are possible. At this time, there is a low chance of the outer coastal waters meeting criteria for a small craft advisory (by frequent gusts >20 kt). Otherwise conditions will remain benign through the period. Seas of 3 to 4 ft will increase to 4 to 6 ft through the weekend into next week, with outer seas potentially reaching 6 to 8 ft. 18/HPR && .FIRE WEATHER...An upper level ridge building over the area late this week and into this weekend will bring a warm and drying trend to western Washington. Periods of offshore flow will be possible throughout Friday and Saturday, which will help dry out fuels from recent rains. Elevated fire weather conditions are expected across portions of the Cascades and areas south of the Sound into the the weekend with high temperatures in the upper 80s to low 90s. Minimum RHs will dip into the 20-30 percent range during the day, with diminished localized values (teens) possible in the Cascade foothills. Overnight RH recoveries will be relatively poor over the weekend due to the aforementioned periods of offshore flow. Warm and dry conditions look to linger into the early half of next week. Mazurkiewicz && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$

972 FXUS66 KPQR 202258 AFDPQR Area Forecast Discussion National Weather Service Portland OR 358 PM PDT Wed Aug 20 2025 .SYNOPSIS...High pressure will build over the region Thursday through the weekend, bringing a prolonged stretch of hot and dry weather with Moderate to Major HeatRisk for inland valleys Friday through Sunday with high temperatures of 95-101F. Remaining warmer than average early next week with a 80-90% chance for high temps of 90F or warmer. Dry and breezy conditions over the southern Willamette Valley Thursday afternoon and early evening will increase fire weather concerns. && .DISCUSSION...Wednesday night through Tuesday night...A significant pattern change begins tomorrow for NW Oregon and SW Washington as a hot and dry conditions begin to develop across the region. This pattern shift is in response to an upper level ridge of high pressure currently centered over the Four Corners region, which will be building northward into the Pacific Northwest. Meanwhile, a thermally induced surface trough in southwest Oregon will shift northward over the Willamette Valley Thursday night into Friday with high pressure east of the Cascades. This set-up will bring a transition from low-level onshore flow to offshore flow, causing an increase in north to northeast winds for the Willamette Valley, Cascades and Columbia River Gorge (except due east in the western Gorge and high Cascades). Max wind gusts are still forecast to reach 20-25 mph, except 30-35 mph in the western Gorge. This will lead to elevated fire weather concerns in some areas, which is discussed below in the fire weather discussion. In regards to forecast temperatures, there hasn`t been much change with today`s update. The deterministic NBM continues to suggest heat will peak Friday and Saturday with widespread highs ranging between 95-101F across inland valleys. Overall model spread is minimal on Friday, suggesting confidence is high to start the heat event. Spread increases a few degrees on Saturday, with the NBM 90th percentile for high temps approaching 105F. Spread increases more considerably Sunday through Tuesday, suggesting confidence is relatively low regarding the exact duration of this heat event (e.g. will it only last 2-3 days, or will it last 4-5 days)? The latest NBM run (21z Aug. 20th) shows NBM 10th-90th percentile values ranging from the upper 80s/lower 90s to the lower 100s on Sunday and Monday, and mid 80s to around 100 degrees on Tuesday. For now, the most likely outcome is for high temps somewhere in the 90s on all three days (80-90% chance). Given the ongoing uncertainty regarding exact temperatures early next week, have left the current timing of the Extreme Heat Watch as is, covering Friday afternoon through Sunday night for inland valleys away from the coast. However, have decided to expand the Extreme Heat Watch to include the south Washington Cascade foothills and the remainder of the Oregon Cascade foothills, as these locations are likely to see temps peak in the 95-100F range with a Moderate to Major HeatRisk. Note these areas will also have mild overnight low temps in the 60s, similar to urban areas in the Willamette Valley. Note the coast is not included in any heat headlines as temperatures will be much cooler there with highs in the 70s. The main reason Major HeatRisk is not more widespread is due to the overnight low temperatures most nights remaining in the low to mid 60s for many locations. However, an increase in those overnight temperatures even 1-3 degrees could result in Major HeatRisk expanding in coverage. Either way, daytime temperatures will be very warm and will impact those who don`t have access to adequate cooling, including those spending time outdoors. If you have extended outdoor plans, especially ones that include strenuous activity, it is important to stay extra hydrated to avoid heat-related illness. Another thing that comes into play early next week is the potential for monsoonal moisture moving into the area from the south, bringing increasing chances for showers and thunderstorms in the Cascades beginning as early as Saturday afternoon or Sunday afternoon when an upper level impulse will push northward towards the Cascades. Note steering flow looks to be very weak, suggesting any storms that do develop would move very slowly. Given the high PWAT values in place (over 1"), heavy rain would be possible with any thunderstorm that develops. As of right now, confidence is very low regarding the exact location and coverage of storms. NBM PoPs are generally around 15% or less, but have the potential to increase with future forecast updates. Even if thunderstorms develop east of the Cascade crest, there is the potential for convective cloud debris to impact high temperatures depending on the coverage and timing. -TK/HEC && .FIRE WEATHER...Expect hot and dry conditions Friday through at least Sunday for areas away from the coast. Critical fire weather conditions are expected to occur over the southern Willamette Valley between 2 and 8 PM Thursday due to dry and windy conditions. During that time, expect northerly winds sustained around 15 mph with gusts up to 25 mph. Relative humidity values will fall as low as 15-25%. Main concern is for rapid fire spread with any grass fire that may ignite. A Red Flag Warning is in effect for fire weather zone 685 from 2 to 8 PM PDT Thursday to cover this threat. Modest easterly winds develop across the Cascade ridgetops and western Columbia River Gorge Thursday night into Friday. Wind gusts up to 35 mph will be possible in the western Gorge during that time. While winds of this magnitude would normally warrant a headline given the dry conditions in place, have decided not to issue any fire weather headlines for the Columbia River Gorge due to the round of wetting rain that fell August 16th. Would be more concerned if the breezy winds were set to occur near or after the end of the upcoming heat event, as fuels would have several more days of hot weather to dry out. Winds weaken beginning late Friday afternoon. Strong nighttime thermal belts will produce poor overnight relative humidity recoveries across the higher terrain Thursday night through at least Saturday night, especially for elevations above 3000 ft where maximum relative humidity values in the 20s and 30s are forecast. Note relative humidity values most likely won`t follow a typical diurnal curve, as humidity values are likely to peak in the evening before dropping rapidly overnight. There is also a 10-15% chance of thunderstorms over the Willamette N.F. near the Cascade crest Saturday through early next week during the afternoon/evening hours each day. Note any thunderstorm that does develop will most likely be slow moving and wet, which would help decrease the potential for widespread new fire starts. -TK && .AVIATION...Dry westerly flow aloft with widespread VFR conditions under mostly clear skies through the remainder of the period. There is a 20% chance of shallow IFR stratus returning to KONP around 12z Thursday. Light surface winds increase out of the north and northwest this afternoon, with gusts up to 20-25 kt along the coast. High pressure builds over the region on Thursday with no concerns. PDX AND APPROACHES...VFR under mostly clear skies through the forecast period. Northwest winds expected around 7-9 kt this afternoon. /Hartsock && .MARINE...High pressure will remain offshore over the northeast Pacific through the remainder of the week and through the weekend. This will maintain northerly winds across the coastal waters, with strongest winds diurnally driven each afternoon and evening as pressure gradients tighten. Expect winds to gust up to 25 kt by late this afternoon south of Cape Falcon. Winds ease a bit by early Thursday morning, then increase again, with gusts up to 25-30 kt, with gusty northerly spreading northward as well. Expect similar conditions through the end of the week. So, have maintained the Small Craft Advisories through Friday afternoon. Seas generally remain wind driven, at around 4 to 6 ft with a dominate period of around 8-9 seconds. /Hartsock && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Extreme Heat Watch from Friday morning through late Sunday night for ORZ108>125. Red Flag Warning from 2 PM to 8 PM PDT Thursday for ORZ685. WA...Extreme Heat Watch from Friday morning through late Sunday night for WAZ204>210. PZ...Small Craft Advisory from 2 PM Thursday to 5 PM PDT Friday for PZZ251-271. Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Friday for PZZ252-253-272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland

670 FXUS66 KMFR 210422 AFDMFR Area Forecast Discussion National Weather Service Medford OR 922 PM PDT Wed Aug 20 2025 .DISCUSSION...Slight alterations were made to the heat products for late this week to group geographically similar areas together into segments. For the details, the product can be viewed at NPWMFR. Heat advisories east of the Cascades end Saturday evening since it appears moisture will increase over there by then along with the chance for showers and thunderstorms. There is some uncertainty with how far west moisture gets, so it will likely stay hotter longer west of the Cascades. As such, Extreme Heat Warnings/Advisories for the west side last through early next week (Monday). First chance of thunderstorms comes Saturday afternoon/evening over portions of the east side as moisture advects northward due to southerly flow on the back side of the Four Corners upper ridge. A weakness off the California coast will allow disturbances to move northward igniting convection first on the Sierra, then into south-central Oregon over the weekend. Model guidance is showing that this pattern of convection over our forecast area could repeat each afternoon/evening Sunday- Wednesday with subtle day-to-day differences in areal coverage/ extent. The upper ridge will gradually weaken through mid-next week and an upstream "kicker" trough is forecast to move onshore around Thursday, pushing the broad moist plume off to the east. This should result in a more typical S-SW flow aloft, drier weather and temperatures trending toward the lower end of "above normal". -Spilde && .AVIATION...21/00Z TAFs...VFR prevails across northern California and southern Oregon and will do so through the TAF period for most areas. The exception would be along the coast north of Cape Blanco where a thin marine layer could return late tonight. The flow could be offshore enough to preclude marine layer development tonight, but if it does develop, it should be confined to the Coquille Basin area and short lived with improvement to VFR is expected by Thursday morning. /BR-y && .MARINE...Updated 830 PM PDT Wednesday, August 20, 2025...The thermal trough will maintain gusty north winds and steep wind driven seas across the waters through the end of the week. Moderate to occasionally strong north winds and brief periods of very steep seas are expected south of Cape Blanco. Winds ease over the weekend, hovering near advisory criteria, but seas are likely to remain steep through the weekend and into early next week. /BR-y && .PREV DISCUSSION... /Issued 449 PM PDT Wed Aug 20 2025/ Updated AVIATION Discussion... AVIATION...21/00Z TAFs...VFR prevails across northern California and southern Oregon and will do so through the TAF period for most areas. The exception would be along the coast north of Cape Blanco where a thin marine layer could return late tonight. The flow could be offshore enough to preclude marine layer development tonight, but if it does develop, it should be confined to the Coquille Basin area and short lived with improvement to VFR is expected by Thursday morning. /BR-y PREV DISCUSSION... /Issued 241 PM PDT Wed Aug 20 2025/ DISCUSSION (Today through Tuesday)... Overview: Noteworthy items for this forecast are as follows: * Heat: A heat wave is expected to start Friday and will likely go through the weekend and potentially into early next week with triple digits possible through this stretch. Heat Advisories and Extreme Heat Warnings are in effect. * Fire Weather: Not seeing an overlap of critical winds and critical RH values, but the heat wave will bring an increased drying trend and critically low RH values. This will result in elevated fire weather concerns, but wind speeds should keep us from any Red Flag Warnings at this time. Please see the Fire Weather discussion below for more information. * Rain/Thunderstorms: Increased chances starting Saturday and continuing into next week. Widespread severe weather not expected, but a couple storms could become strong with lightning and strong outflow winds as the main hazards. Further Details: Not much has changed in regards to the upper levels. We will have a broad area of high pressure consuming much of the southern CONUS while hurricane Erin is currently east of this area. Hurricane Erin will push north and disrupt the high pressure to the west and northwest which will result in height rises over our forecast area through later parts of this week as Erin gets absorbed into the main flow. This will result in a very warm airmass with triple digit temperatures expected through the end of the week and potentially into early next week. Heat Advisories and Extreme Heat Warnings start Friday. The peak of the heat wave will be Fri-Sun, and records will be within reach for several official climate sites. The placement of the high pressure will allow for monsoonal moisture to get pulled northward. At the same time, we will have weak perturbations riding the northern periphery of this high pressure. The combination of upper level energy and moisture could result in precipitation across mainly eastern parts of the forecast area Saturday through Monday. Saturday being the least areal extent. Any shift in the high pressure could result in the energy aloft and moisture getting diverted in either a positive or negative manner as far as precipitation goes. Will continue to monitor this threat. At this time, widespread severe weather does not appear likely, but if a thunderstorm forms it could become strong with lightning and strong outflow gusts (45-55 mph) as the main threats. These storms would be tied very closely to daytime heating, so these would likely be pop-up storms through peak heating (2pm-8pm) as we reach convective temperatures. The combination of convective temperatures and small impulses aloft should be enough to trigger thunderstorms this weekend into early next week. -Guerrero MARINE...Updated 200 PM PDT Wednesday, August 20, 2025...As the thermal trough rebuilds across the area today, expect gusty north winds and steep seas south of Cape Blanco through this evening. These steep seas will expand to all area waters later this evening. These conditions will persist through the weekend, with moderate to occasionally strong north winds and brief periods of very steep seas south of Cape Blanco. FIRE WEATHER...Updated 200 PM PDT Wednesday, August 20, 2025... A weak upper shortwave is bringing just enough instability to develop cumulus over area terrain, with little to no chance for any more significant activity. Beyond the shortwave, seasonal warmth and dry conditions continue today. High pressure developing over the Four Corners area looks to build an upper ridge over the area starting Thursday and remaining in place through at least the weekend. The most immediate effect will be temperatures rising 5-15 degrees above seasonal norms. An Extreme Heat Warning has been issued for Friday afternoon through Monday evening, affecting FW Zones 619, 620, 622, 280, 281, 282, and 284. A Heat Advisory is in place for Friday afternoon into Saturday night for other inland areas. Individuals in these zones who are not prepared for these hazardous conditions may experience heat-related illnesses. Dry conditions continue for Thursday through the weekend as well. Overnight recoveries look to be generally moderate, but periods of easterly flow overnight could bring locally low recoveries to area peaks and ridgelines. This looks especially true for terrain in western Siskiyou County, and may affect Curry County coastal ranges as well. Monsoon moisture looks to move over the area on Saturday morning. With ample surface heating expected, convective thunderstorm development will be possible east of the Cascades and in northern California starting on Saturday afternoon and evening. In general, the best chances look to be in easternmost Lake and Modoc counties, with lesser chances over other areas east of the Cascades and possibly into Siskiyou County as well. Additional instability remains absent from the forecast, although this could change as information gains detail. Without additional instability, convective thunderstorms tend to be isolated to locally scattered in coverage. Winds aloft look to be light, which may limit storm motion. With the amount of moisture anticipated, any thunderstorms that develop may be wet which would help reduce the threat of fire starts. -TAD && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Extreme Heat Warning from 1 PM Friday to 8 PM PDT Monday for ORZ024-026. Heat Advisory from 1 PM Friday to 8 PM PDT Saturday for ORZ023- 025-027>031. CA...Extreme Heat Warning from 1 PM Friday to 8 PM PDT Monday for CAZ080-081. Heat Advisory from 1 PM Friday to 8 PM PDT Saturday for CAZ082>085. PACIFIC COASTAL WATERS...Small Craft Advisory until midnight PDT Friday night for PZZ350-356-370-376. && $$ MAS/JWG/TAD

257 FXUS66 KEKA 202018 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 118 PM PDT Wed Aug 20 2025 .SYNOPSIS...The warming and drying trend will continue with intensification Thursday and Friday. Inland temperatures warming from 100 to 110 late this week and through the weekend will create fire weather concerns and a Moderate to locally Major HeatRisk. Hot temperatures will continue into next week. There is a very slight potential for thunderstorms over the interior this weekend, with higher chances likely early to mid next week. && .DISCUSSION... Key Points: -Significant and long duration hot temperatures will bring Moderate to Major HeatRisk inland Thursday and into next week -The hot and dry weather will bring fire weather concerns -Monsoonal moisture will bring a very slight potential for thunderstorms over the interior this weekend, with higher chances early to mid next week Temperatures will continue warming with a strengthening Four Corners Region high. Inland temperatures will make a substantial jump upward Thursday when the once displaced high fills back in after the passage of a shortwave trough. This will be in sharp contrast to the recent trend of below to much below average inland high temperatures, giving less time for acclimation. For this reason, and the hot temperatures of 100 to 110 combined with warm overnight lows, there is a Moderate to some areas of Major HeatRisk. There will be some troughing that will attempt to dig south over the ridge Sunday, but any weakening of the strong high will be a slow process. Heat Advisories are out starting Thursday and lasting through Saturday evening. Extensions of the advisories in select zones may be required. Please exercise caution with outdoor activity and learn the signs of heat exhaustion or stroke. The Four Corners region high will tap into monsoonal moisture at the end of the week. Monsoonal moisture will begin clipping the eastern region starting Friday. There is a small but impactful chance (5-9%) for isolated dry thunderstorms starting Sunday for Trinity County. There looks to be a good amount of convective inhibition (CIN) at that time. Chances for thunderstorms look to then trend higher early through likely mid next week with additional monsoonal moisture. There will eventually be higher precipitable water values and a better chance for precipitation in any shower or thunderstorm the reach the ground, but moistening through the very dry column will be a slow process. A very weak low level inversion has been allowing the shallow marine stratus to remain quite disrupted and fully cleared over the land through some periods. The inversion will strengthen, particularly Friday and through the weekend. This pattern favors a more resilient and shallower marine stratus layer and better chances for fog. JJW && .AVIATION...(18Z TAFs)...Stratus has started to nudge away from the coast late this morning, leaving behind VFR conditions and breezy northwest winds. Building high pressure will complicate stratus development this evening and overnight. Some likely will form, with models suggesting some forming around Humboldt Bay then advecting northward to ACV and CEC, bringing IFR or LIFR ceilings and visibilities. If the marine layer ends up being too shallow, and a few models do suggest this possibility, offshore flow aloft could keep stratus away from the terminals. Regardless, any stratus that does form is likely to scatter out by late morning. Inland areas, including UKI, are likely to remain VFR for the next 24 hours period. JB && .MARINE...Northerly winds have picked up as high pressure builds over the area. Winds will be strongest in the lee of Cape Mendocino and around Pt. St. George, with near-gale to localized gale force gusts possible this afternoon and Thursday afternoon. Steep seas of 7-10 ft will accompany the strongest winds. Despite much lighter winds in most nearshore areas, some propagation of the seas are possible south of Cape Mendocino today and across the area Thursday. Winds also increase slightly Thursday, which has prompted a short- fused Gale Warning in the southern outer waters Thursday afternoon. A gradual improvement in winds and seas are expected into the weekend. Waves are currently dominated by a 3 to 4 foot wave at 10 seconds, which will continue to gradually diminish through the day today. A small southwest wave around 15 seconds is expected has filled in this morning and will linger into the weekend. && .FIRE WEATHER...Building hot and very dry weather over the next several days will generally increase fire danger and dry fuels back out after several days of relief. Though light rain last weekend was enough to moisten fine fuels, live and larger fuels continue to be near peak dryness for all interior areas. RH late this week will drop to some of the lowest of the season so far with some single digit minimum RH possible in the feat eastern interior. Gusty northeast winds will develop over the ridges of interior Del Norte County tonight through Thursday morning. Beyond hot and dry weather, the main concerns will be for potential thunderstorms late in the week and this weekend. Heat will greatly increase surface instability, but moisture will generally be lacking to generate thunderstorms. By around Sunday, there is some indication of monsoon moisture wrapping around and up into the Central Valley, but the general pattern will be much more conducive to storms over the central Sierras (20% chance there) rather than NW California (only 5% thunder chance here). There is some potential for a more concerning pattern around next Monday, and likely into mid next week with moisture possibly wrapping back out to the coast. This potential will have to be watched closely. JHW/JJW && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Heat Advisory from 11 AM Friday to 11 PM PDT Saturday for CAZ105-106-110-113. Heat Advisory from 11 AM Thursday to 11 PM PDT Saturday for CAZ107-108-111-114-115. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 PM Thursday to 5 AM PDT Friday for PZZ450. Small Craft Advisory from 4 PM this afternoon to 2 AM PDT Friday for PZZ455. Small Craft Advisory from 11 PM this evening to 11 AM PDT Saturday for PZZ470. Small Craft Advisory until 3 PM PDT Thursday for PZZ475. Small Craft Advisory from 11 PM Thursday to 11 AM PDT Saturday for PZZ475. Gale Warning from 3 PM to 11 PM PDT Thursday for PZZ475. && $$ NOTE: The full forecast discussion is now regularly issued between 10 am/pm and 1 pm/am. Additional updates will be issued as needed. 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

703 FXUS66 KMTR 210351 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 851 PM PDT Wed Aug 20 2025 ...New UPDATE, MARINE, FIRE WEATHER... .KEY MESSAGES... Updated at 1216 PM PDT Wed Aug 20 2025 - A Heat Advisory is in effect from Thursday - Friday for much of the interior Bay Area and Central Coast. - Temperatures will remain above normal through the weekend. - Elevated fire weather conditions across the interior Thursday into the weekend. && .UPDATE... Issued at 833 PM PDT Wed Aug 20 2025 Satellite imagery shows a patch of stratus along the immediate Pacific coast from Half Moon Bay down to Davenport. A Heat Advisory will go into place for the interior Bay Area and Central Coast at 10 AM Thursday. For the North Bay valleys and the San Francisco Bayshore, the Advisory continues through Thursday night, while across the rest of the interior Bay Area and Central Coast, the Advisory extends through Friday night. One of the main motivations for extending the area under Heat Advisory was temperatures running far above the forecast today across the Bayshore regions. For example, Oakland Airport and San Francisco Airport reported highs of 82, while Redwood City reported a high of 95. The respective forecast highs today were 78, 76, and 87. Even if Thursday`s highs don`t similarly overshoot the current forecast, the fact that this is going to be the first widespread warming of the summer season, rather later in the summer compared to the patterns last year, will result in people not being as acclimated to the heat as they were this time last year. Or in layman`s terms, people haven`t seen temperatures this hot so far this summer. This will result in an increased risk of heat- related illnesses, especially for vulnerable populations including children, the elderly, pregnant women, people with certain chronic illnesses, and anyone working or living outdoors without adequate cooling or hydration. DialH && .SHORT TERM... Issued at 1216 PM PDT Wed Aug 20 2025 (This evening through Thursday) Temperatures are currently around 5 degrees warmer than this time yesterday with a few more hours of heating in store this afternoon. Even in the short term, the temperature forecast has been a bit of a challenge. The cooler than normal Summer seems to have made a negative impact on the NBM bias correction. Out of roughly 1000 observations yesterday, 444 were at or above the NBM 90th percentile for max temperature. That fact had me all geared up to use the NBM 90th percentile as the baseline for the forecast, until I saw the output. It was just too hot to pass the sanity check. 117 F at Tassajara can certainly happen, but probably not with a 25C 850 temperature. Fortunately the deterministic NBM has increased a bit from yesterday, likely as a result of the cool bias we`ve seen recently. There is also a complicating factor of high clouds rolling in tomorrow. The first sign of the incoming monsoon moisture will be in the upper levels. The 300 mb RH was last measured at 4% and is expected to be over 95% in the next 24 hours. This will surely bring some amount of upper level clouds, which have a slight cooling effect during the day. The coverage, timing and opacity of these clouds are hard to pin down, however. After much analysis, I decided to increase the deterministic NBM max temperatures by one degree Fahrenheit for all land areas from Thursday-Saturday. && .LONG TERM... Issued at 1216 PM PDT Wed Aug 20 2025 (Thursday night through next Tuesday) The high clouds Thursday actually have a warming effect at night by trapping some IR radiation. This effect, combined with continued building of the ridge and 850 temperatures will cause overnight lows to stay in the upper 50s to low 60s for most, and even mid 70s at higher elevation starting Thursday night. That`s about 5 degrees warmer than normal for the low-lands, and up to 15 degrees warmer in the mountains. Typically, even under ridging conditions, clear skies bring a strong nocturnal inversion and cool mornings at the surface, but the extra humidity and clouds will limit that effect this time. The max temperatures and HeatRisk have also trended up Fri-Sat, and it`s likely we will have to extend some or all of the Heat Advisory into Saturday. This monsoon moisture, combined with conditionally unstable lapse rates above 700 mb, bring a small chance for elevated convection starting Friday. There is no clear trigger for this instability to be realized, and thunderstorms will likely be confined to higher elevations in the Sierra. The instability and moisture look to wane by Sunday, but the NBM probability of thunder sticks around (albeit less than 5%) through the forecast period. The heat will gradually improve through early next week with temperatures eventually settling near normal. Even this will feel warm for many as we approach the warmest time of the year after a relatively cool Summer. && .AVIATION... (00Z TAFS) Issued at 452 PM PDT Wed Aug 20 2025 VFR through the TAF period. Winds reduce into the evening and become mostly light across the region into the night. Some spotty pockets of low clouds and fog look to affect portions of the coast overnight and into Thursday morning, but don`t look to fill over any of the TAF sites. WInds build again into Thursday afternoon becoming moderate for most areas and breezy at SFO. These winds look to reduce again that evening. Vicinity of SFO...VFR through the TAF period. Winds reduce and gusts cut off into the night, with only moderate west winds expected through the night and most of the morning. West winds rebuild into the mid to late morning on Thursday with gusts peaking around 22 kts. Winds and gusts reduce again going into Thursday night. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR through the TAF period. Winds become light in the late evening and stay light through Thursday afternoon. Moderate west and northwest winds build for Thursday afternoon with some infrequent gusts. These winds become light again that night. && .MARINE... (Tonight through next Tuesday) Issued at 833 PM PDT Wed Aug 20 2025 Expect elevated seas to continue along with breezy to gusty northwest winds will prevail through Friday morning, especially across the outer waters and coastal jet regions near Point Sur and Point Reyes. This will result in widespread hazardous conditions for small craft. Wind and seas will begin to gradually ease Friday afternoon and evening, leading to calmer conditions over the weekend and well into the next work week. && .FIRE WEATHER... Issued at 833 PM PDT Wed Aug 20 2025 Elevated fire weather threats are expected to begin on Thursday, with hot and dry conditions resulting in curing of fuels, especially across the interior where the combination of poor overnight humidity recoveries, very poor daytime humidity retention, and warm overnight lows in the higher elevations will bring little relief from the drying trend. ERC and Burning Index forecasts continue to show drying fuels and the possibility of large fires to take hold and spread rapidly. In addition, we are monitoring a surge of monsoonal moisture set to arrive on Friday through the weekend, which will bring a very low, but non-zero, chance for elevated convection across the Central Coast. Fire weather conditions improve in the early part of next week as a gradual cooling trend takes hold. DialH && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 10 AM Thursday to 10 PM PDT Friday for CAZ504- 510-512>518. Heat Advisory from 10 AM to 10 PM PDT Thursday for CAZ506-508. PZ...Small Craft Advisory until 3 AM PDT Thursday for Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 3 PM Thursday to 9 AM PDT Friday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm- Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory until 9 AM PDT Friday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...Murdock MARINE...Murdock Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea

931 FXUS66 KOTX 202210 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 310 PM PDT Wed Aug 20 2025 .KEY MESSAGES... - Dry and breezy southwest winds through Wednesday evening with elevated fire weather conditions. - Warm and dry through the weekend and into next week with much of Central WA and the L-C Valley in areas of Major HeatRisk with isolated areas of Extreme HeatRisk. && .SYNOPSIS... Winds will be breezy through Wednesday evening with elevated fire weather conditions. Then a persistent ridging pattern will lead to a warming and drying trend across the region Thursday into next week. && .DISCUSSION... Wednesday evening: Breezy westerly winds will continue through the Cascade gaps and across the Columbia Basin into the evening hours, then will subside after sunset. Thursday through Tuesday: A warming and drying trend will prevail from Thursday onward as a ridge of high pressure amplifies over the region. Temperatures will peak Saturday through Tuesday with afternoon highs in the mid 90s to low 100s and limited overnight relief with lows only dropping into the mid 60s to mid 70s. An Extreme Heat Watch has been issued for Saturday afternoon through Tuesday evening across the Columbia Basin, Okanogan Valley, Methow Valley, and L-C Valley. Avoiding strenuous outdoor activities and consuming plenty of water and electrolytes will be important to protect yourself from heat-related illnesses. Pumpkin spice may be returning soon, but summer is not over. /Fewkes && .AVIATION... 00Z TAFS: VFR conditions will prevail for all sites through the next 24 hours. Breezy west winds with gusts up to 20kts will continue through the evening. Winds will subside after sunset tonight (around 03Z). FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for conditions to remain VFR. ----------------------- 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:/weather.gov/otx/avndashboard && .Preliminary Point Temps/PoPs... Spokane 84 53 87 54 91 57 / 0 0 0 0 0 0 Coeur d`Alene 84 53 87 54 90 58 / 0 0 0 0 0 0 Pullman 80 51 85 51 91 53 / 0 0 0 0 0 0 Lewiston 90 61 93 60 98 63 / 0 0 0 0 0 0 Colville 85 44 86 45 90 48 / 0 0 0 0 0 0 Sandpoint 82 49 85 50 87 52 / 0 0 0 0 0 0 Kellogg 81 57 83 58 90 60 / 0 0 0 0 0 0 Moses Lake 87 52 88 55 94 59 / 0 0 0 0 0 0 Wenatchee 85 60 88 63 93 67 / 0 0 0 0 0 0 Omak 88 55 88 56 93 59 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... WA...None. ID...None. && $$

629 FXUS66 KPDT 210013 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 513 PM PDT Wed Aug 20 2025 .AVIATION...00Z TAFs...VFR conditions are forecast for all sites through the valid period. Breezy winds through the Cascade gaps are expected to decrease in magnitude this evening. Winds of 10 kts or less are then anticipated at all sites overnight through Thursday, albeit with periodic afternoon gusts to 15 kts mainly at PDT/RDM/BDN. Plunkett/86 && .PREV DISCUSSION... /issued 344 PM PDT Wed Aug 20 2025/ DISCUSSION...Today, quiet weather persists with seasonable high temperatures across our region with daytime RHs in the 20s and 30s. Locally breezy winds (15-25 mph) may develop over the Columbia River Gorge and Kittitas Valley this afternoon. Winds will then start to drop tonight with seasonable min temps. As the high pressure system starts to build over Thursday, temps will continue slightly increasing by a few degrees above normal as the daytime RHs trend downward. Winds will generally remain light to breezy with gusts under 25 mph. Widespread fire weather concerns are expected due to RHs and winds not meeting their critical thresholds. Friday into next week will be hot and drier as the high pressure system approaches across our region with the dry airmass. Breezy winds with low RHs remains overlapping from the Gorge down to Central OR for Friday. From there, this had elevated our fire weather concerns that led us to issuing a Fire Weather Watch from Friday afternoon into the evening. With the ridge axis moving directly over the forecast area, we may have a potential heatwave event for Saturday through Tuesday that will increase high temps to the upper 90s and low 100s. This will also lead to moderate to major HeatRisk for Saturday, but mainly major for Sunday onwards across the Columbia Basin area. The Euro and GFS members are in good agreement with these temps during those days, which boosted our confidence into issuing an Extreme Heat Watch from Saturday afternoon through Tuesday evening. Daytime RHs will keep trending downward into the teens and low 20s with light winds. There is a slight chance (<20%) of thunderstorms developing over the southern portion of the eastern mountains Sunday into Wednesday from the ongoing influence of the monsoonal moisture. Best chances for development would be at Deschutes County to the Southern Blues Sunday into Monday. Although these storms could become wet, there is not enough moisture support hence thus leaving the storms to be dry with abundant lightning as the potential main threat. Feaster/97 && .PRELIMINARY POINT TEMPS/POPS... PDT 54 89 56 94 / 0 0 0 0 ALW 60 90 61 96 / 0 0 0 0 PSC 54 91 54 96 / 0 0 0 0 YKM 55 89 59 94 / 0 0 0 0 HRI 55 91 56 96 / 0 0 0 0 ELN 51 86 54 93 / 0 0 0 0 RDM 45 90 49 96 / 0 0 0 0 LGD 51 89 53 95 / 0 0 0 0 GCD 51 90 53 98 / 0 0 0 0 DLS 57 93 62 98 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Fire Weather Watch from Friday afternoon through Friday evening for ORZ691-703. Extreme Heat Watch from Saturday afternoon through Tuesday evening for ORZ041-044-507-508-510. WA...Extreme Heat Watch from Saturday afternoon through Tuesday evening for WAZ024-026>029-521-523. && $$ SHORT TERM...97 LONG TERM....97 AVIATION...86

044 FXUS65 KREV 201903 AFDREV Area Forecast Discussion National Weather Service Reno NV 1203 PM PDT Wed Aug 20 2025 .KEY MESSAGES... * Warming trend continues with peak heat and Major HeatRisk in lower elevations Friday through Friday night. * Monsoonal moisture brings shower and thunderstorm chances to parts of the eastern Sierra and western NV by Friday afternoon. * Widespread moisture will bring increased shower and thunderstorm chances from this weekend through the middle of next week, along with a cooling trend. && .DISCUSSION... Dry air mass hangs on through the next couple of days, although the increase of cirrus clouds overnight into Thursday will signal the start of a changing weather pattern. An expanding ridge of high pressure extending from the eastern Great Basin to the southern Rockies will begin to draw in more moisture starting Friday afternoon, with south flow aloft setting up across the Sierra and western NV. Temperatures will also reach their peak levels on Friday, with highs pushing to near or above 100 degrees in many lower elevations of western NV and northeast CA. This will be followed by a warm night as cloud cover thickens, with lows ranging from the mid 60s-lower 70s. Heat advisories will remain in effect as the combined effect of the daytime and overnight temperatures raises the HeatRisk to the Major category. A slight cooling will begin on Saturday with more extensive cloud cover, although temperatures will remain about 4-8 degrees above average. The first round of showers and thunderstorms associated with the moisture return is projected to begin Friday afternoon, with the most favored areas including Mono, Mineral and Lyon counties (20-40% chances). Lesser chances (10-20% chances) spread north and west across parts of west central NV, far western NV and Alpine county, and may reach into the Reno-Carson-Minden areas and near Tahoe, depending more on outflow interactions and surface convergence. While some elevated fire concerns are possible as these storms develop (see the Fire Weather section below for more details), the primary concerns will be heavy downpours that could produce localized flash flooding, along with frequent lightning, gusty winds and small hail. The main window for these storms will be in the 2-9 PM time frame, although a few showers could continue overnight especially for Mono-Mineral counties. For this weekend, the coverage of showers and thunderstorms expands across the remainder of western NV and eastern CA, especially by Sunday. The main areas of concern will remain over the eastern Sierra and western NV south of US-50 where chances increase to 50-70%. However, any storm will be capable of producing periods of moderate to heavy rain with possible flash flooding if storms persist in steep terrain, burn scars or urban areas, along with gusty outflow winds, frequent lightning and small hail. One limiting factor with high moisture content is the potential for the formation of a thick cloud shield that limits instability, and transitions a thunderstorm pattern into areas of lighter rain showers as the afternoon progresses. Next week, showers and thunderstorms are likely to continue especially Monday and Tuesday where an upper low off the CA coast could bring additional forcing into the pre-existing moist environment. Depending on where/how much rain occurs over the weekend, more areas could become more at risk for flooding if more storms occur in these areas. The precip chances then look to decrease later next week. With the weakening and retreat of the upper ridge to the south central US, temperatures will trend downward with highs mainly in the mid-upper 80s for lower elevations and 70s for Sierra communities from Tuesday onward. MJD && .AVIATION... VFR conditions with mainly light winds continue through Thursday. Heat continues to increase each day leading to density altitude concerns for western NV terminals, peaking on Friday. Isolated thunderstorm chances return to the main terminals Friday afternoon, with the best chances at KMMH. Daily shower and t-storm chances return to all terminals each afternoon from this weekend into the middle of next week. MJD && .FIRE WEATHER... Dry conditions with a warming trend prevail through Thursday. The heat peaks on Friday, while increasing moisture will bring isolated-scattered thunderstorm chances Friday afternoon to the eastern Sierra and parts of western NV, mainly south of US-50. While precipitable water values will increase relatively quickly to between 0.75-1" and favor wetter storms, the initial 1-2 hours of storms could be accompanied by dry lightning strikes and gusty outflow winds. Afterwards, the influx of deeper moisture and the potential for moderate to heavy wetting rainfall should limit the likelihood of dry lightning to the periphery of rain cores on Saturday and beyond. MJD && .REV Watches/Warnings/Advisories... NV...Heat Advisory from noon Friday to 9 AM PDT Saturday NVZ001- 003>005. CA...Heat Advisory from noon Friday to 9 AM PDT Saturday CAZ071. && $$

433 FXUS66 KSTO 201942 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 1242 PM PDT Wed Aug 20 2025 For additional details on weather and expected impacts over the next 7 days, please visit weather.gov/sto/briefing. .DISCUSSION... .SYNOPSIS... Our warming trend continues and as a result a Heat Advisory remains in effect for the Valley, Delta, and adjacent foothills for Friday and Saturday for triple digit highs and widespread Moderate HeatRisk with areas of Major HeatRisk. Elevated fire weather conditions accompany the heat with daily mountain thunderstorm chances Friday into next week over the Sierra. && .KEY MESSAGES... * Today - Thursday: - Above normal temperatures expected with widespread Valley triple digits and Moderate HeatRisk by Thursday. - Periodically breezy north winds overnight into Thursday AM may provide localized enhanced drying over the Nor. Sacramento Valley and see areas of elevated fire weather conditions from dry and hot weather. * Friday - Saturday: - A Heat Advisory has been issued for the Valley, Delta, foothills and Coast Range from 11 AM Friday through 11 PM Saturday. - High temperatures in the upper 90s to triple digits expected through the Valley/foothills, with limited overnight relief. - Probability of Valley/foothills high temperatures > 100F Fri- Sat: 65-100% - Widespread Moderate HeatRisk and areas of Major HeatRisk expected Friday-Saturday, followed by a gradual cooling trend into early next week. - Dry weather with low daytime humidity in the teens to 20s and limited overnight recovery anticipated mlate week. This will continue periods of elevated fire weather conditions. - Monsoonal moisture advection will bring chances of afternoon/evening thunderstorms to the Sierra crest south of I-80 Friday into the weekend. Thunderstorm chances expand northward Saturday and Sunday with best chances for development on Saturday. Current models show a lack of forcing mechanism that could develop into a larger thunderstorm threat but storms riding the ridge and moving north and east are in play. * Sunday to Early Next Week: - Slight cooling trend is expected, but widespread Moderate HeatRisk still persists across the Valley and foothills Sunday and Monday with a return to Minor HeatRisk by Tuesday. - Isolated mountain thunderstorm chances (10-25%) over the Sierra through early next week. .Changes from previous forecast... - No significant changes at this time. && .AVIATION... VFR conditions next 24 hours across interior NorCal. Sustained surface winds generally at or below 12 kts, except in the Delta with west-southwest surface winds 12-15 kts with gusts 15 to 20 kts through 16Z Thursday. && .STO WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM Friday to 11 PM PDT Saturday for Carquinez Strait and Delta-Central Sacramento Valley-Mountains Southwestern Shasta County to Western Colusa County-Northern Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley. && $$

575 FXUS65 KMSO 201859 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 1259 PM MDT Wed Aug 20 2025 .DISCUSSION... KEY MESSAGES: - Chance for thunderstorms this afternoon for Lemhi County, Silver Bow County - Heat this weekend - Chances for thunderstorms Sunday and Monday for southwest Montana and Lemhi County Satellite imagery this afternoon indicates a well-formed low pressure circulation spinning along the British Columbia-Alberta border north of the northwestern U.S. This feature will keep the Northern Rockies under southwesterly flow aloft today. Furthermore, this circulation will send a weak (and dry) cold front through north-central Idaho and western Montana this afternoon. The front will bring some gusty westerly winds region- wide and provide some instability for afternoon thunderstorms. Instability supportive of storm development, however, will be limited to Lemhi County and southwest Montana, with lesser chances along the Continental Divide. Westerly flow aloft will take over on Thursday as the Canadian low moves east and south. By Thursday night, the low will be east of the Divide. This system will push a weak backdoor cold front over the Divide, resulting in a wind shift to easterly winds for northwest Montana. East or northeast winds will propagate through western Montana later on Friday. A strong ridge of high pressure will build over the Northern Rockies on Saturday. Most ensemble solutions are in good agreement that this will be a prolonged period of high pressure, lasting well into next week. Daytime high temperatures will rise to about 5-10 degrees above normal for Saturday. The lower valleys of western Montana will reach the upper 80s to low 90s, while the lower Salmon and Clearwater valleys will see triple digits. Monsoonal moisture will make its way into the southern portion of the Northern Rockies on Sunday as a Four Corners high strengthens through the weekend. Available moisture will bring chances for thunderstorms to north-central Idaho and southwest Montana on Sunday and Monday. && .AVIATION... Gusty west winds will develop at all airfields this afternoon with the passage of a dry cold front. Expect westerly gusts of about 20-30 knots. KBTM and KSMN could see some thunderstorm activity after about 20/2200Z. VFR conditions will persist through Thursday as high pressure begins to build through the weekend. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...Red Flag Warning until 10 PM MDT this evening for East Beaverhead. ID...None. && $$

331 FXUS65 KBOI 210254 AFDBOI Area Forecast Discussion National Weather Service Boise ID 854 PM MDT Wed Aug 20 2025 .DISCUSSION...The weak shortwave has moved northeast out of the region, with flow aloft veering from southwest this evening to westerly by early Thursday. Skies will remain mostly clear aside from smoke from local fires in Owyhee County, Idaho and Valley County, Idaho, as well as the Cottonwood Peak Fire in Elko County, Nevada. The largest smoke plume continues from the Cottonwood Peak Fire, spreading northeast mainly east of a line from Owyhee, Nevada to Mountain Home, Idaho and Atlanta, Idaho. West-northwest winds on Thursday should help keep additional smoke from this fire southeast of the area. High pressure will rebuild Friday with the ridge axis shifting over eastern Oregon. This will bring a return of hot temperatures across the Intermountain West through the weekend, along with monsoonal moisture from the Southwest to support thunderstorm development. && .AVIATION...VFR. Local visibility reductions in central and s- central ID due to wildfire smoke. Surface winds: W to NW 5-15 kt. Gusts to 20-30 kt from KBKE-KONO and portions of Treasure Valley this evening. Then, variable 10 kt or less overnight. Winds aloft at 10kft MSL: SW to W 10-20 kt. KBOI...VFR. Surface winds: W to N 5-12 kt. && .PREV DISCUSSION... SHORT TERM...Tonight through Friday night...Hints of shortwave troughing will move NE out of the area overnight tonight. In its wake, a "cold" front will move through SE OR and SW ID late this afternoon into evening. Breezy winds, with gusts 20-25 kts, will impact the Treasure Valley. Beginning Thursday, persistent ridging, courtesy of the Four Corners High, will begin to slowly build. As it does so, flow aloft will transition to more westerly Thursday and then southerly on Friday. Warm and dry conditions will persist Thursday and Friday. High temperatures will begin near normal today and Thursday, and increasing to 5-10 degrees above normal Friday. Hints of monsoonal moisture will creep into the ID/NV and OR/NV border area beginning late Friday into Saturday. Less than a 10% chance of precipitation exists south of the Western Magic Valley late Friday. Smoke from wildfires will continue, mainly in the West Central Mountains and near the ID/NV border. LONG TERM...Saturday through Wednesday...The Four Corners High will redevelop over the region, bringing above normal temperatures and a monsoonal push of moisture through the beginning of the long term period. The main concern will be late Saturday into Monday with the juxtaposition of dry surface air and very moist upper levels. This will create a prime environment for critical fire weather conditions with scattered dry lightning from any high based convection that forms. Current models favor moisture in southeast Oregon and near the ID-NV border, but there is still uncertainty in areal extent of the moisture. By Tuesday, ensembles favor near record high PWAT values (~1.15-1.3 inches of water) which would bring widespread precipitation to the region. There is still quite a bit of uncertainty on this moisture and how far north into our region it will push, but long term outlooks favor above normal precipitation through Wednesday , especially for areas south and west of the Snake River Valley. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise DISCUSSION...JDS AVIATION.....SH SHORT TERM...CH LONG TERM....SA

189 FXUS65 KLKN 201123 AAA AFDLKN Area Forecast Discussion...Updated National Weather Service Elko NV 423 AM PDT Wed Aug 20 2025 .KEY MESSAGES... Updated at 423 AM PDT Wed Aug 20 2025 * Elevated fire weather conditions for Eastern Nevada today * A warming trend is expected Thursday and Friday * Heat Advisory for most of Northern and Central Nevada Friday * Wetting thunderstorms likely in Eastern Nevada each afternoon and evening Sunday through Tuesday && .UPDATE... Issued at 423 AM PDT Wed Aug 20 2025 Updated for the issuance of a Heat Advisory. && .DISCUSSION... (Today through Tuesday) WEATHER PATTERN OVERVIEW: An upper-level area of high pressure will remain parked over the Four Corners region of the United States today through Saturday. Isolated, dry thunderstorms are expected in Eastern Nevada this afternoon into this evening. A few of these thunderstorms could be strong. The primary thunderstorm hazards will be wind gusts near 50 mph and dangerous cloud to ground lightning strikes. A warming trend is anticipated Thursday and Friday. By Friday afternoon, high temperatures will be seven to nine degrees above normal for this time of year. This type of heat will result in a moderate risk for heat-related illnesses. Although heat events like this are relatively common and happen many times a year, heat-related impacts are possible for those new to the area if simple precautions are not taken. A Heat Advisory is in effect for most of Northern and Central Nevada Friday. A Heat Advisory may be required for Northern Nevada Saturday. The aforementioned anticyclone aloft will shift southward Sunday through Tuesday. Monsoonal moisture will move northward into Eastern Nevada Sunday through Tuesday, resulting in the likelihood of wetting thunderstorms each afternoon and evening. A cooling trend trend is anticipated Sunday through Tuesday. By Tuesday afternoon, maximum temperatures will be around five degrees below seasonal values. FORECAST CONFIDENCE & DEVIATIONS: High forecast confidence in elevated fire weather conditions for Eastern Nevada today. High forecast confidence regarding a warming trend Thursday and Friday. High forecast confidence in a Heat Advisory for most of Northern and Central Nevada Friday. Moderate forecast confidence regarding wetting thunderstorms in Eastern Nevada each afternoon and evening Sunday through Tuesday. No deviations from the NBM model output. && .AVIATION... VFR conditions are forecast for at all terminals through Wednesday. Conditions Wednesday will see partly cloudy skies during the afternoon as increasing mid level moisture will allow for convective build-ups for KELY, KEKO, KENV and KBAM. Winds will be out of the SW at 10KT to 20KT with gusts up to 30KT possible. && .FIRE WEATHER... Elevated fire weather conditions expected in Eastern Nevada this afternoon and this evening due to southwest to west wind gusts near 25 mph and minimum relative humidity values as low as 8 percent. Isolated, dry thunderstorms are anticipated in Eastern Nevada this afternoon into this evening. A few of these thunderstorms may be strong. The primary thunderstorm hazards will be erratic wind gusts near 50 mph and dangerous cloud to ground lightning strikes. Isolated, dry thunderstorms are expected in White Pine County Thursday afternoon into Thursday evening. Wetting rain is likely in Eastern Nevada Sunday through Tuesday. && .LKN Watches/Warnings/Advisories... Heat Advisory from 11 AM to 8 PM PDT Friday NVZ030-031-036>038-041. && $$ DISCUSSION...87 AVIATION...98 FIRE WEATHER...87