Graphical Hydro Meteorological Discussion

554
FXAK68 PAFC 201402
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 AM AKST Fri Dec 20 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Sunday)...

The trailing shortwave from yesterday`s gulf low is currently
pushing through the area, bringing a brief period of steadier
precipitation to the Prince William Sound. This light rain and
mountain snow will taper off this morning in the lull between
storms. For today, expect similar conditions to yesterday, though
slightly warmer as increasingly warm air moves into the region.
The next system will first impact Kodiak Island with gusty
northeasterly winds, picking up this evening, followed by rain.
The leading shortwave and surface front will then reach the Sound
around midnight tonight, beginning a period of light to moderate
precipitation along the Gulf Coast, particularly the eastern Kenai
Peninsula. With the low track well to our south, ample amounts of
warm air have been able to move east of the storm, which will
raise snow levels to 2000 to 2500 ft. For the Sound, expect nearly
continuous light to moderate, and occasionally heavy, rain
through the weekend as multiple systems take a similar track from
the North Pacific to near Kodiak Island.

For inland areas the main forecast question is surface temperature
and precipitation type. The 12Z Anchorage sounding is now firmly
into the freezing rain profile, and will likely remain this way
for the foreseeable future. Generally speaking, the upcoming
system will be mostly downsloped, however there will be multiple
periods where there is strong enough upper level dynamics and
enough moisture that rain and/or freezing rain is likely to fall
in the lee of the mountains for areas like Anchorage, the western
Kenai north of Kasilof and the Mat Valley. Currently, this looks
most likely late Saturday night. Temperatures will slowly warm
through the day on Saturday, reaching highs between 29 and 36
degrees for the aforementioned areas. Regardless of the surface
temperature, area roadways that are currently snow covered or have
surface temperatures below freezing are likely to get icy. This
doesn`t look like a cold enough setup for true freezing rain that
will accumulate on surfaces like power lines, but area roadways
are likely to become slick (or even more slick than they already
are if we`re being honest...). There are still some uncertainties
to work out for Sunday and Monday, but really it looks like more
of the same, coastal rain and chances for rain and freezing rain
for the Cook Inlet areas and Mat Valley. The Interior of
Southcentral should remain dry.

-CJ

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS
(Days 1 through 3: Today through Sunday night)...

The underlying pattern that has already been in place for the past
several days is poised to continue well into the weekend. Several
lows will continue to parade from east to west from the Gulf into
the eastern Bering Sea through early next week, each carried by
easterly flow situated on the northern side of a sprawling,
complex upper level trough stretching across much of the North
Pacific and Bering region. One of these lows is now moving
offshore from the AKPen (Alaska Peninsula) this morning and
westward into the Bering Sea. A few light showers are clipping the
northern side of Bristol Bay on the northern periphery of this
circulation, but otherwise dry and cool conditions are in place
across most of Southwest north of the low. This current system
will weaken as it approaches the Pribilofs later this evening, but
could still drop a quick inch of wet snow before continuing
northwest and effectively shearing apart late tonight.

Attention will then shift to the next low in the continued east-
west low track, which will be a much larger and stronger system
moving south of Kodiak Island by early Saturday. North to
northeast winds will quickly pick up across the AKPen and much of
Southwest, with gales picking up ahead of the low both near
Bristol Bay and to the south of the AKPen throughout the day
Saturday as the low marches west. Precipitation will overspread
portions of Bristol Bay as well as the AKPen and eastern Aleutians
as the low begins to slow down and nearly stall out close to the
Shumagin Islands by Saturday evening. However, strong cross-
barrier flow developing across the Alaska/Aleutian Ranges will
limit how much rain/snow can reach the surface across the Lower
Kuskokwim Valley and Bristol Bay through Sunday morning. Better
chances for precipitation will be focused across northern Bristol
Bay near the Kilbucks, including Dillingham and Togiak. Quite a
bit of warmer air aloft will be transported in from the east as
the low approaches, but cold air in place over valleys with
persistent northerly winds at the surface could yield a profile
supportive of sleet and freezing rain, most likely along an axis
from Koliganek to Dillingham Saturday evening. Confidence for
seeing any measurable freezing rain is still low, but is
beginning to increase.

Forecast details begin to fall apart late Sunday into early
Monday as yet another low with a more uncertain track begins to
pinwheel up from the Pacific into Kodiak Island and the Alaska
Peninsula from the southeast. Despite the track spread, this low
does not look like it will be as intense as the previous in the
series, and may even begin to merge with the prior system still
drifting over the eastern Bering by Sunday night. Out along the
Aleutians, more benign conditions will finally turn more inclement
as a deep North Pacific low pushes a strong front into the
Aleutian Chain by late Sunday night.

-AS

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

The long term forecast begins with a low in the Gulf centered
near Kodiak Island. This low will allow for a Gale or possibly a
Storm Force barrier jet to form along the Southcentral coastline.
Gusty winds could even extend into the Barren Islands, and
Shelikof Strait regions. This will all depend on the exact
location and strength of the low which is still uncertain at this
time. As for the West, A col forms over the central Aleutians near
Adak with a deep low to the west. The low will allow for storm
force winds and precipitation in the Shemya region. As the low
travels east, gale force winds will affect the Bering as well as
gap winds Alaska Peninsula near Cold Bay on Tuesday.

Back to the Gulf for Wednesday has a low pushing in from the
Southwest. There is quite a bit of uncertainty regarding its
track, but gale force winds and precipitation are expected to
accompany the low. Upslope flow along the Southcentral coast and
mountainous regions will likely trigger heavier precipitation, but
areas more inland including the Anchorage Bowl will likely stay
on the dry side due to downsloping. A barrier jet may form with
the passage of the low, but like before, this will depend on the
strength and track it decides to take, which is uncertain at this
time. Winds will die down by Thursday as the low dissipates as it
moves inland. As these winds calm down, downsloping will end and
precipitation will finally be able to make it into the Anchorage
Bowl, but exact QPF is uncertain. In the West for Wednesday, the
low will open into an upper level trough and will funnel cold air
from the north. This will allow gale force winds to linger in the
waters west of the Pribilofs and for widespread light snowfall to
occur across the central Bering and into the Kuskokwim Delta
coast. Thursday has cold air advection continuing to filter down
and the 0F line will pass the Aleutian islands, allowing for
widespread but light snowfall. Also, A low will arrive from the
southeast, which has some implications, but it`s track is still
too uncertain to make any hard predictions.


-JAR


&&

.AVIATION...

PANC...VFR conditions and northerly winds will persist.
Southeasterly winds to around 25 kt aloft will lead to weak wind
shear through the afternoon.

An approaching front will bring another surge of easterly to
southeasterly 20 kt winds aloft beginning early Saturday morning.
Weaker downsloping with Saturday`s storm could bring the potential
for freezing rain as early as 12Z Saturday, with precipitation
forecast to change over to rain around 00Z Saturday as surface
temperatures warm up.

&&


$$

095
FXAK69 PAFG 201135
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
235 AM AKST Fri Dec 20 2024

.SYNOPSIS...
A series of lows moving across the Alaska Peninsula and into the
southern Bering Sea through the weekend and strong high pressure
over Siberia results in a tightening pressure gradient through the
Bering Strait to St. Lawrence Island. Very strong north to
northeast winds develop from Point Hope to St. Lawrence Island.
Wind gusts approaching or over 70 mph are possible this weekend
into next week.

&&

.DISCUSSION...

Key Messages...

Central and Eastern Interior...
- Tanana Valley Jet remains active, with gusts to near 45 mph in
Delta Junction today. Southerly gap winds to 45 mph in the AK Range
passes,diminish this evening and tonight and then increase again on
Saturday.

- On Saturday, east to northeast winds increase over Interior
summits, especially over the Dalton Highway summits, where winds
will gusts to near 35 mph. These winds will cause areas of blowing
snow that will reduce visibility at times Saturday and Saturday
night.

- Warming trend this weekend with high temperatures in the single
digits to teens above zero by Sunday.

- Light snow blossoms over the northern Interior (Yukon Flats)
Sunday afternoon into the overnight and may continue at times
into early next week.

North Slope and Brooks Range...
- Stratus and areas of fog persist across the Arctic coast this
morning will slowly diminish today.

- Very strong northeast winds develop along the Western Arctic Coast,
primarily southwest of Point Lay this weekend. Gusts of 60 to 70
mph are looking more likely in Point Hope Sunday into Monday.

- Gusty north to northeast winds of 30 to 40 mph develop through
western Brooks Range passes Saturday and Sunday. Further east,
through Anaktuvuk and Atigun passes, north winds of 15 to 20 mph
expected.

West Coast and Western Interior...
- Northerly gales develop today in the Bering Strait and
strengthen to near storm force late Saturday. Wind gusts near
or over 70 mph are possible from Point Hope to St. Lawrence
Island Sunday and Monday. This will result in rapid sea ice growth
and a potential for light freezing spray on St. Lawrence Island.

- Across the remainder of the coast, north to northeast winds will
gust to 40 to 50 mph. Northeast winds with gusts to 45 mph expected
across the Noatak Valley Sunday.

- Generally dry conditions through the weekend. By late Sunday night
into Monday snow chances begin to increase over the Western
Interior.

Analysis and Forecast Confidence...
Upper level ridging persists from Siberia southeast to the
southern Yukon Territory and southeast Alaska. An upper level low
north of Prudhoe Bay weakens as it slowly tracks eastward to the
Northwest Territories through Saturday. An upper level low in the
high Arctic drops southeast across the Arctic waters Saturday
afternoon into Sunday with a shortwave trough extending southeast
across the North Slope and Brooks Range. A series of lows will
move out of the far northern Pacific and Gulf of Alaska and across
the Aleutians into the southern Bering Sea.

At the surface, a weak low near Point Thomson weakens as it moves
east of Mackenzie through Saturday. High pressure over the
Northwest Territories and the Yukon moves southeast and weakens
through the weekend, maintaining the Tanana Valley Jet and gusty
winds at Eagle. A series of low will move out of the Gulf of
Alaska, across the AK Peninsula and into the southern Bering
through the weekend and into next week. As these lows move into
the Bering, high pressure over Siberia strengthens, tightening the
pressure gradient over the Bering Strait with winds gusts of 60
to 70 mph developing from Point Hope to St. Lawrence Island. As
these lows lift northwest, they push a series of weak fronts
across the Alaska Range and into the Interior this weekend into
early next week. The combination of these fronts and a trough
dropping out of the Arctic will increase snow chances Sunday night
into mid-week from the eastern Beaufort Sea coast to the Brooks
Range and into the northern Interior from Fort Yukon to the Seward
Peninsula.

Latest model guidance is showing a slightly weaker gradient this
weekend due to weaker ridging over Siberia. Nevertheless, strong
northerly winds are expected from the Chukchi Sea south through
the Bering Strait and to St. Lawrence Island this weekend into
early next week. Forecast confidence remains high for winds.
Forecast confidence is lower when it comes to snow amounts,
placement, and timing Sunday into next week.

Extended Forecast Days 4-7...
The extended forecast features weak ridging aloft over the eastern
Interior with upper level lows in the high Arctic and in the
north Pacific to Aleutians. Sensible weather wise, strong
northerly winds with gusts approaching storm force possible
through the Bering Strait to St. Lawrence Island Sunday into mid-
week. Models struggle with the placement, timing, and amount of
snow. There will be plenty of moisture with this system and
wherever it develops, it will likely remain stationary for a few
days. This could result in a wide swath of heavy snow. The
heaviest snow looks to fall over central and eastern Brooks Range
to Bettles and southwest towards Unalakleet. High temperatures
largely on the positive side of zero south of the Brooks Range
through Wednesday before plummeting as cold air associated with
upper trough pushes to the Interior.

Coastal Hazard Potential Days 3 and 4...
Strong northerly winds develop through the Bering Strait this
weekend. Coastal erosion is the main concern at this time.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...High Wind Watch for AKZ801.
High Wind Watch for AKZ820-821.
High Wind Watch for AKZ827.
PK...Heavy Freezing Spray Warning for PKZ801-807-854.
Small Craft Advisory for PKZ801.
Brisk Wind Advisory for PKZ802.
Brisk Wind Advisory for PKZ803>806-850-852-853.
Brisk Wind Advisory for PKZ810-811-857.
Gale Warning for PKZ816-817-851-854.
Heavy Freezing Spray Warning for PKZ816-817.
Heavy Freezing Spray Warning for PKZ851.
Gale Warning for PKZ856.
&&

$$

851
FXAK67 PAJK 201416
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
516 AM AKST Fri Dec 20 2024

.SHORT TERM.../Through Friday/...
The active pattern continues, although a brief lull in the
precipitation will move from S to N through the day on Friday
ahead of another system which will advance N into the southern
panhandle by Friday afternoon.

The most recent system has largely fallen apart as it advances
north across the panhandle. The frontal band`s distance from the
low, along with lingering cold air outflow in the inner channels,
meant that the system has all but disintegrated as it moves into
drier air across the central and northern panhandle. One result of
this has been that cooler temperatures have lingered near the
surface across much of the area. This has resulted in periods of
freezing rain across parts of the Icy Strait Corridor and
Petersburg as the decaying system`s warm front (and corresponding
warm air advection) has largely pushed over the cooler air near
the surface, rather than displacing it entirely. Winter Weather
advisories are out for parts of the area through the morning hours
on Friday as a result, though only expect minor ice
accumulations.

In the wake of the system, a brief lull in the pattern will emerge
later in the day on Friday, with stronger northerly outflow re-
establishing itself. Another system arriving Friday afternoon into
Friday night will see winds briefly flip out of the S across most
of the area barring the northern panhandle, alongside a wave of
rain and wind which will race northward, though these will be
strongest in the southern panhandle. By late Friday night, winds
across the central inner channels will once more be starting to
flip back out of the N as said frontal band`s impact fades, and N
outflow tries to re-establish itself once more.

Temperatures will finally start to warm across the central and
northern panhandle Friday afternoon, though the far northern
panhandle will likely hold on to cooler temperatures longer.
Primary forecast changes were to emphasize wind shifts in the
inner channels, as well as increasing wind speeds - especially
across the outer coastal waters and across land-based locations in
the southern half of the area. Also added the possibility of a
freezing rain rain/snow mix in for Juneau, Gustavus, and
Petersburg through parts of the morning on Friday. Delayed the
timeline for warming temperatures across the central and northern
panhandle on Friday, although do still expect the warmup to happen
- just a little slower than previously progged.

.LONG TERM.../Saturday through Thursday/...
Overview: SE AK will be impacted by a series of strong lows
moving into the AK Gulf from the south then tracking west. These
systems will bring in warm temperatures, moderate to heavy rain
fall, and strong winds. Gulf winds will be a gale to storm force
with small craft to gale force winds over the inner channels at
least. Overland winds gusts along the southern and coastal areas
of 40 to 50 mph at least expected Temperatures may near record
values for this time of year which will keep precip as rain with
the exception of the Haines and Klondike highway borders where at
least a few inches of snow accumulation are probable.

A mid level low is the main steering force for the mid range that
keeps these surface low pressure systems entering the area. While
the mid level low varies as smaller waves rotate around it not
seeing any movement from the area until late next week. Extreme
Forecast Index has been consistent the past few runs depicting
the warm swath of air moving in into next week. High temps in the
low to mid 40s with possible 50s, if the 90th percentile is
accurate. Current record highs for this time of year are mostly in
the upper 40s to mid 50s. EFI has the stronger winds along the
southern and coastal areas for Sunday then again Wednesday. Gusts
of 40 to 50 mph likely but as most of the fronts as associated
with lows pulling back to the west have lower confidence in gusts
of 60 mph or higher.

Ensembles depicting consistent features with the operational
indicating some differences early on. GFS has been consistently
on the high side for winds but started to see NAM and Canadian
fall in line with higher gulf winds Sunday.


&&

.AVIATION...Flying conditions this morning continues to be very
much location dependent. For the far northern panhandle and NE
Gulf coast, VFR conditions continue to be persistent with some
MVFR developing. Farther south, conditions become less favorable
with MVFR CIGs and an area of freezing rain currently across the
PAGS to PAJN area at the time of writing. This area of freezing
rain is currently expected to persist through the morning before
warming temperatures and diminishing precip cut off precip. From
Sumner Strait southward, IFR to VFR CIGs this morning and are
spreading northward slowly ahead of the next front. With the next
front moving in, CIGs and VIS are expected to remain in the IFR to
MVFR range for the southern panhandle. LLWS is expected to spread
across the panhandle with this front and is expected to make it
as far north as the Icy Strait corridor including PAJN. AAWU
forecasts for the panhandle show that turbulence and icing will
also become more of an issue as the front moves from north to
south during the TAF period.


&&

.MARINE...Elevated winds continue across the maritime areas, with
gale force winds across the outer coastal waters and small craft
conditions at times across the inner channels expected to last
through the weekend.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory until 9 AM AKST this morning for AKZ320-
325.
Strong Wind this evening for AKZ323.
Winter Weather Advisory until 6 AM AKST early this morning for
AKZ326.
Strong Wind from noon AKST today through this afternoon for
AKZ328.
Strong Wind from 3 PM AKST this afternoon through this evening
for AKZ330-332.
MARINE...Gale Warning for PKZ641>644-652-661>664-671-672.
Small Craft Advisory for PKZ012-013-021-022-031-033>036-053-651.

&&

$$

SHORT TERM...GFS
LONG TERM....PRB
AVIATION...SF
MARINE...GFS

Visit us at http://www.weather.gov/Juneau