Graphical Hydro Meteorological Discussion

676
FXAK68 PAFC 211239
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
339 AM AKST Thu Nov 21 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...

The dominant feature for Alaska Weather is a strong closed upper
level ridge centered along the southern Alaska Peninsula.
Anticyclonic flow and associated sinking motion extends across
the eastern Bering Sea and all of southern Alaska and the Gulf
of Alaska, leading to "bone dry" conditions. Warm (above freezing
air) aloft moved over the ridge into Southcentral yesterday. The
airmass has warmed further due to northerly downslope flow along
the east side of the ridge. A look at temperatures across
Southcentral mountain locations bears this out, with above
freezing temperatures from Hatcher Pass to the western Chugach
Mountains to the Kenai Mountains. The warmest temperatures are
over the eastern Kenai Peninsula Mountains, with widespread 40s.
Meanwhile, temperatures down at sea level remain well below
freezing with single digits below zero in the southern Susitna
Valley to single digits (above zero) and teens as you head south
to the Kenai Peninsula. The exception is coastal locations like
Whittier, Seward, and Kodiak where downslope winds are mixing
down the warm air to the surface. The airmass over the Copper
River Basin remains quite a bit cooler, with temperatures well
below zero in the Copper Valley. Robust low level northerly flow
along the east side of the ridge is combining with surface
pressure gradients to maintain fairly strong and gusty winds along
coastal gaps. The steep temperature inversion in place on the
eastern Kenai Peninsula seems to be promoting downward
acceleration of the winds along the coast, with wind gusts as high
as 50 to 60 mph in both the Seward and Whittier areas.

The weather will remain quite stagnant for the next few days as
the ridge remains upstream of Southcentral. The ridge center will
slowly shift southward into the North Pacific, but anticyclonic
flow over Southcentral and the Gulf will remain strong. Today will
likely be the warmest day in the mountains, with slight cooling
as a ridge axis over Southcentral shifts south late today.
However, the areas which are above freezing now will likely remain
there. Inland valleys will see a slight warming, but will largely
remain below freezing. Gap winds will keep going along the coast,
though as the ridge shifts a bit further east this weekend, low
level flow will weaken and pressure gradients will loosen. This
will lead to weakening of all coastal gap winds. Other than some
occasional mid to high clouds passing through, conditions will
remain dry.

-SEB

&&


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

The large ridge over the eastern Bering will begin to weaken with
the core shifting south into the North Pacific Friday and
Saturday. Low stratus and fog will continue this morning for
portions of the Kuskokwim Delta and Lower Kuskokwim Valley with
the potential for it to linger into Friday morning. The one
caveat against fog is that surface winds will turn northeasterly
and off-shore today which could advect in slightly drier air from
the interior helping to lower dew points. However, the overall
airmass and ridge position today into Friday morning will change
very little. Elsewhere across Southwest, expect mostly scattered
high clouds today through Saturday.

A series of shortwaves continues to deliver light rain and
southeast winds to the Western Aleutians this morning. This
activity is expected to clip Adak later today. A shortwave coming
off of Kamchatka will interact with a shortwave in the North
Pacific late this evening into Friday morning and cause a surface
low to spin up across the Western Aleutians Friday morning. This
will help to enhance showers and winds across the both the
Western and Central Aleutians Friday as the front pushes eastward
with time. Pockets of gale-force winds are possible across the
Central Aleutians Friday with mostly small-craft winds expected.
Pockets of gale-force winds are expected across the western
Bering Friday evening into Saturday morning on the backside of the
system.

The initial front weakens as it reaches the Pribilof Islands
Saturday. However, the main trough across the western Bering will
begin to dig further into the North Pacific Saturday afternoon and
evening which will help pull more moisture northward. This
additional moisture surge looks to mainly affect portions of the
Central Aleutians (Atka) and the Pribilof Islands with steadier
rain late Saturday night into Sunday. The front also makes it to
the Kuskokwim Delta coast and Nunivak Island Saturday and remains
stationary into Sunday morning. The resulting weather for now
looks to be showers for Saturday with potentially more wide-spread
and steadier rain for Sunday across the Kuskokwim Delta coast.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

The Alaska Weather map will become a bit more elastic and active
as a strong shortwave ripples across the top of the Interior
Alaska upper level ridge through Tuesday. The Bering shortwave
extending from an Anadyr low moves over the ridge into Canada for
Tuesday. The ridge resets over the Western Mainland through
Wednesday. Areas of moderate rain and some gusty winds spread over
the Western and Central Aleutians on Sunday before the system
moves over the Bering. This system will turn Eastward, briefly
flattening the ridge. Most of the Southern Interior is expected to
have light winds, overall dry conditions and somewhat moderate
temperatures in the zonal flow over the lower half of the state,
although coolest overall temperatures should linger over the
Eastern Interior through Tuesday. Precipitation, if any, will be
light and intermittent through the weekend with a very small and
brief risk of freezing precipitation over Interior locations.


&&.AVIATION...

PANC...VFR conditions and light winds will persist.

&&


$$

567
FXAK69 PAFG 211301
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
401 AM AKST Thu Nov 21 2024

.SYNOPSIS...High pressure is building after 3 frontal passages
across the area the past couple of days. Moisture is trapped at
the surface, particularly along a line from Nome to Galena to
Fairbanks beneath a decaying cold front, making freezing drizzle
the main forecast concern through today. A number of Winter
Weather Advisories are in effect for a light glaze of ice
accumulation. Very high pressure building over the Arctic Plain overnight
tonight will push remaining moisture south, though areas of fog
and stratus will remain south of there. The Arctic Coast will
clear today and overnight tonight. The next frontal system looks to
bring significant snow to the West Coast beginning late Saturday
and pushing into the Interior on Sunday.

&&

.DISCUSSION...
Key Messages...

Central and Eastern Interior...
- There remains a slight chance of freezing drizzle through this
morning across the Tanana Valley. Reports of freezing drizzle
overnight have been isolated and travel may be difficult in
localized areas as a result. Widespread impacts are not
expected.

- Southeast winds are gusting to 40 mph at Eagle and are expected
to remain gusty through early this morning. A Wind Advisory
remains in effect through this morning.

- About 1 inch of snow is expected for the Tanana Valley through
today.

- Wind and blowing snow over Eagle Summit will diminish after noon
today. Have extended the Winter Weather Advisory until then.

- North winds gusting to 30 mph are expected through Alaska Range
passes overnight tonight into Friday morning.

- Dry, mild, and partly cloudy to mostly clear conditions are
expected beginning Friday.

- The next chance for significant snowfall will be Sunday
afternoon through Monday night.

North Slope and Brooks Range...
- West winds and blowing snow across the Eastern Arctic Coast
diminish today.

- Quieter and colder conditions expected through the weekend,
though east winds increase Saturday evening along the coast.

- Periods of clearing today and Friday, even along the coast.

- North winds around 15 mph through Brooks Range Passes ease early
Friday morning.

West Coast and Western Interior...
- Winter Weather Advisories for Nome, Golovin, and Eastern Norton
Sound remain in effect until 6PM Thursday for freezing drizzle.

- Drier conditions expected after Thursday. Temperatures remain
well above normal, with many areas near the coast seeing high
temperatures near or above freezing through the weekend.

- The next frontal system looks to bring significant snow to the
West Coast beginning late Saturday and pushing into the Interior
on Sunday.

- Strong northerly Gales are expected through the Bering Strait
early next week behind the frontal system.

High pressure is firmly in place over northern Alaska, trapping
remnant moisture from multiple frontal passages yesterday at or
near the surface. A strong ridge aloft continues to be centered
over Bristol Bay with surface high centers near the Kuskokwim
Delta and Dawson City, Yukon. High pressure will remain in place
through Thursday, continuing chances for light freezing drizzle
mainly along the line of the weakening cold front from Nome to
Galena to Fairbanks. Beginning Thursday evening, very strong high
pressure will build over the North Slope. This will push remaining
moisture south of the Alaska Range, though areas of fog and
stratus will likely remain through Friday. Strong high pressure at
the surface and ridging aloft through Saturday will keep
conditions quiet and dry across the area. The next chance for
widespread precipitation will be Saturday afternoon at the West
Coast as a strong shortwave begins to break down the ridge. This
shortwave and associated precipitation will push into the Interior
Sunday through Tuesday.

Forecast changes tonight were minor. Have extended the Winter
Weather Advisory for Eagle Summit for blowing snow and low
visibility through noon today. The Winter Weather Advisory for the
Eastern Arctic Coast remains in effect through 6am this morning,
but anticipate that should not need to be extended. Otherwise,
just updated the near term for fog and freezing drizzle where it
is being reported. Delayed the timing of the Saturday-Tuesday
shortwave in the PoP and wind fields by about 6 hours to align
with the latest model guidance.

Extended Forecast For Days 4 Through 7...The extended forecast
period beginning Sunday afternoon will start with a moisture laden
shortwave producing significant snowfall west of a line from
Fairbanks to Deadhorse. This system will spread east through
Tuesday night and may bring upwards of 6 inches of snow to parts
of the Interior. There is still a lot of uncertainty in snow
amounts, and that forecast will be refined as the event
approaches. Another strong ridge looks to build over the state
following this system, bringing strong inversions to the Interior
and above normal temperatures with dry conditions elsewhere.

Coastal Hazard Potential Days 3 and 4...None.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Winter Weather Advisory for AKZ829-830-834-839>846-852.
Winter Weather Advisory for AKZ822-824.
Wind Advisory for AKZ835.
Winter Weather Advisory for AKZ805.
PK...Heavy Freezing Spray Warning for PKZ806.
Heavy Freezing Spray Warning for PKZ807.
Small Craft Advisory for PKZ812.
Heavy Freezing Spray Warning for PKZ812.
Brisk Wind Advisory for PKZ813-859.
Brisk Wind Advisory for PKZ814.
Brisk Wind Advisory for PKZ815-861.
Small Craft Advisory for PKZ851.
Heavy Freezing Spray Warning for PKZ856.
Heavy Freezing Spray Warning for PKZ857.
Brisk Wind Advisory for PKZ858.
Brisk Wind Advisory for PKZ860.
&&

$$

CHRIEST

764
FXAK67 PAJK 211229
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
329 AM AKST Thu Nov 21 2024

.SHORT TERM.../Through Thursday/... The forecast remains largely
unchanged, with an ongoing outflow even likely to continue through
the remainder of the week. A broad area of ridging over Alaska
remains entrenched, as a blocking pattern increasingly takes hold
with sharp areas of troughing on either side serving to mitigate
any imminent departure of the ridge. For SE AK, this means that
cold weather, clear skies, and wind look set to continue. The wind
will at least marginally diminish in some areas for much of
Thursday as the pressure gradient weakens somewhat in conjunction
with a decaying low located W of Washington State. However, the
decaying low will be replaced by a new low as cyclogenesis occurs
along the SE periphery of the trough axis, and so expect
wind speeds to begin ramping back up again by Thursday night into
Friday.

Still anticipate windy conditions for many land-based locations,
though think that at least for downtown Juneau and Douglas, wind
gusts will drop below 60 mph beyond early Thursday morning. Only
minimal changes were to made to the forecast - mainly to
temperatures through the current time frame in order to reflect
the (somewhat) warmer conditions caused by turbulent mixing.
Forecaster confidence is above average.

.LONG TERM.../Friday into early next week/... Blocking pattern
developing over the region means that conditions will remain
relatively unchanged through the weekend and into early next week
across the panhandle. High pressure will continue over the
interior, though may shift further east into British Columbia by
the start of next week. This could lead to a slight weakening of
northerly outflow winds, but enhance outflow winds from NE and
easterly oriented valleys and interior passes.

Any chance of precipitation returning to the panhandle rests on the
blocking ridge over the western gulf breaking down. Deterministic
models are attempting to do so, or at least weaken the ridge such
that a short wave can develop in the northern gulf. If this comes to
fruition, snow showers could be expected along the outer coast
sometime Monday into Tuesday with the potential to reach into the
Icy Strait corridor and central panhandle. However, ensembles
guidance are still leaning towards the ridge remaining strong into
early next week. For those looking for more snow, this potential
trough early next week looks to be fairly dry with ensemble
guidance suggesting 24 hr snow totals of 1.5 to 2.5 inches by
Wednesday.

This far out, there is a high confidence in the overall synoptic
pattern with outflow winds continuing and relatively dry conditions
through the weekend. With no significant storms currently showing up
in model guidance in the mid and long range, the blocking ridge
could be around for a while, which means generally below normal
temperatures and continuing dry conditions potentially into the
Thanksgiving holiday.

&&

.AVIATION...VFR SKC with outflow winds continuing. LLWS and
turbulence through the morning before winds at ridgetop diminish
for a few hours. Expect elevated NE winds at ridgetop to return
Friday.

&&

.MARINE...Gale force outflow winds through northern inner
channels and interior passes/river valleys for the northeast gulf
coast, and out of Cross sound. With the persistent winds in Lynn
Canal and down Chatham Strait, have enhanced seas through
Thursday. Winds diminish a bit on Thursday for some of the inner
channels before intensifying again late Thursday night into
Friday.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind through this afternoon for AKZ318.
Strong Wind until 6 AM AKST early this morning for AKZ319.
High Wind Warning until 6 AM AKST early this morning for AKZ325.
Strong Wind from 6 AM this morning to noon AKST today for AKZ325.
MARINE...Gale Warning for PKZ012-013-031-644.
Small Craft Advisory for PKZ011-022-032>036-641>643-651-652-
661>664-671-672.

&&

$$

SHORT TERM...GFS
LONG TERM....STJ
AVIATION...GJS
MARINE...GFS
HYDROLOGY...99

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