312
FXAK68 PAFC 210148
AFDAFC
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 PM AKST Fri Dec 20 2024
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Monday)...
Southcentral Alaska is in the lull between storms this afternoon
with shower activity along the coast and in the western Susitna
Valley rapidly clearing out. A North Pacific low is beginning to
push a front into the southern Gulf which will bring another round
of gusty northeasterly winds and moderate to heavy rain beginning
tonight. The front also lifts to the north Gulf coast by midnight,
beginning a period of light to moderate precipitation,
particularly for the eastern Kenai Peninsula. Southeasterly flow
brings in ample amounts of warm air, raising snow levels up to
2000 to 2500 ft. Along the north Gulf coast, expect nearly
continuous light to moderate rain, heavy at times, to persist
through the weekend as a series of lows and fronts lift into the
southern Gulf and track into the vicinity of Kodiak Island.
Warm air has already worked in aloft over portions of inland
Southcentral even as surface temperatures remain in the 20s.
Temperatures gradually increase around the Cook Inlet region as
warm air filters in slowly tonight and tomorrow, plateauing near
freezing by Saturday afternoon and hovering around there likely
through Monday. This makes for a complicated forecast in
combination with the generally downsloped precipitation pattern
which will see multiple periods where there is strong enough
upper-level dynamics provided by passing shortwave troughs and
enough moisture that rain and/or freezing rain is likely to fall
in the lee of the mountains for areas of the western Kenai north
of Kasilof, Anchorage, the Matanuska Valley, and the southern
Susitna Valley up through Willow. Currently, the best chance for
this overspreading precipitation is Saturday evening into the
overnight hours, with the potential for a few hundredths of an
inch of liquid precip. Regardless of whether the surface
temperature is above or below freezing, area roadways that are
currently snow-covered or have surface temperatures below
freezing are likely to get icy and area roadways may become
slick.
There are still some uncertainties to work out for Sunday
and Monday, but really it looks like more of the same, with
coastal rain and continued chances for light/intermittent rain
and freezing rain for the Cook Inlet areas and Mat Valley. There
is some indication that the Copper River Basin, which remains much
colder, could see light snow on Sunday and Monday, with the
greatest chance for accumulation along the western portions of the
basin near Eureka and Tahneta Pass.
CJ/CQ
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS
(Days 1 through 3: This afternoon through Monday evening)...
The active weather pattern looks to continue across the Bering
Sea, Aleutians, and Alaska Peninsula through Monday. The main
culprit, which is a broad negatively tilted trough, continues to
remain draped across the Bering, Aleutian Chain, and down into the
North Pacific. A meso-low continues working northwestward across
the eastern Bering. This system continues to bring light snow to
the Pribilof Islands. However, as this system moves north of the
islands tonight, winds will turn south and any leftover
precipitation will fall as rain/snow mix.
The next low lifts northward towards the AKPEN for Saturday. While
most precipitation will be confined to the Pacific side of the
AKPEN, there will be a series of shortwaves that lift northward
and over mainland Southwest. These shortwaves will also bring
warmer air aloft over the area. The best chances for precipitation
will be around the Bristol Bay and Kuskokwim Bay coasts. Surface winds
will remain out of the northeast with easterly to east-
southeasterly winds aloft bringing in the warmer air. Thus, this
setup is favorable for a wintry mix across Bristol Bay and the
Kuskokwim Delta. A Winter Weather Advisory has been issued for
Bristol Bay from Dillingham north and west from Saturday afternoon
until Sunday morning for a mix of light snow and light freezing
rain. A Winter Weather Advisory has also been issued for the
Kuskokwim Delta from Sunday evening until mid-Sunday morning for a
mix of snow, sleet, and freezing rain. The air column around the
Kuskokwim Delta looks to be a little bit cooler than that of
Bristol Bay with the best chance of snow/sleet accumulation from
Bethel and west. Meanwhile, the best chance for freezing rain
accumulation resides along the Kuskokwim Bay Coast. Meanwhile,
additional weak shortwaves look to continue move across Southwest
for Monday which could help light wintry mix/freezing rain to
persist across the area; especially for Bristol Bay.
Farther out west, the Aleutian Chain will also continue to remain
unsettled through Monday as numerous shortwaves continue to move
across the Bering helping to keep rain/snow showers going across
the area. A bigger and stronger system arrives for Sunday night
into Monday morning as a North Pacific low and front approach the
Western Aleutians. The storm-force front looks to mainly affect
the marine zones on the North Pacific side of the Western
Aleutians. Moderate to heavy rain accompanying the front will
spread from the Western Aleutians to the Central Aleutians by
Monday afternoon and evening, as will gale-force winds.
&&
.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...
Gale force winds will be present across much of the Bering Sea on
Tuesday due to the influence of cold air advection and a low
south of the Shemya region. Southcentral will be much calmer in
comparison with southerly winds continuing to keep temperatures
warmer than average. Light precipitation is relegated to the
Southcentral coasts and Kodiak Island as weak troughing will
linger in the region. Wednesday swings a low from the south into
Southcentral. This low will move northward and despite some
uncertainty in exactly what track it will take, guidance is
indicating that it will be somewhere near Kodiak Island by
Thursday. Impacts include gale to storm force winds moving with
the low and a potential for a barrier jet to set up once its
pressure gradients move up to the Southcentral coast. Other
impacts are heavy precipitation along the coasts and Kodiak
Island. The positioning of the low will initially prevent
precipitation from making it more inland due to the mountains
blocking moisture flow.
The west sees a different picture for Wednesday and Thursday. An
Arctic trough will sweep down and continue to cause cold air
advection to take place all across the western domain. Convective
but light snow showers will be widespread all across the Bering. A
line of snow will stretch from the North Slope all the way down
to the Kuskokwim Delta through Thursday. Temperatures will plummet
for the southwest mainland through Saturday and the GFS is
indicating that some locations in the Lower Kuskokwim Valley could
see temperatures as low as -40F by the end of the forecast
period. Looking back to Southcentral for Friday has the
aforementioned low linger through the end of the forecast period.
This, combined with the cold temperatures to the west could allow
for a nice setup for snowfall in the Anchorage Bowl and the MatSu
Valley regions as the low shifts and allows moisture to flow in.
This is quite uncertain and changes in the low`s positioning and
cold air to the west could prevent this scenario from taking
place.
-JAR
&&
.AVIATION...
PANC...VFR conditions and northerly winds will persist.
Southeasterly winds increasing to around 30 kt or greater aloft
will lead to the development of low level wind shear beginning
early Saturday morning.
A weaker downsloping signal with the storm system on Saturday
could bring the potential for light freezing rain as early as 12Z
Saturday, with precipitation forecast to change over to rain
around 00Z as surface temperatures warm up.
&&
$$
308
FXAK69 PAFG 202238
AFDAFG
Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
138 PM AKST Fri Dec 20 2024
.SYNOPSIS...
Strong northerly winds will develop this weekend from St. Lawrence
Island through the Bering Strait. A number of lows will rotate
into the Southern Bering from the Gulf of Alaska, paired with a
slightly anomalous high pressure sitting over Far Eastern Russia.
This will create a pressure gradient through the Bering Strait.
Winds gusts associated with that pressure gradient will approach
70 mph. These winds will persist into early next week.
&&
.DISCUSSION...
Key Messages...
Central and Eastern Interior...
- Tanana Valley Jet will remain active through Saturday night.
Wind gusts will be near 45 mph at Delta Junction through this
time period. They will slowly diminish starting Saturday
morning. Southerly gap winds in the Alaska Range up to 45 mph
will persist through Saturday.
- The Dalton Highway Summits will begin to see increasing
northeasterly winds starting overnight tonight. Winds will gust
up to 35 to 40 mph, and cause periods of blowing snow along the
Dalton Highway.
- Sunday morning, heavier snowfall will begin to develop in the
northeastern interior from Tanana to Arctic Village.
Accumulations on Sunday and Monday will look to be around 4" to
6". There are possibilities that snowfall will continue through
much of the week, but there is significant uncertainty as to
where exactly the band of heaviest snowfall will set up.
North Slope and Brooks Range...
- The Western Arctic Coastline will see strong northeasterly winds
of 60 to 70 mph develop Saturday evening. This will be
primarily focused near Point Hope and to the southwest offshore.
- Anaktuvuk and Atigun pass will have 20 to 25 mph northerly
winds develop Sunday morning and last through the day. The
Western Brooks Range will have gusty northeasterly winds up to
45 mph this weekend.
West Coast and Western Interior...
- Gale force northerly winds will develop overnight tonight. The
strongest core of winds will be from St. Lawrence Island to the
Bering Strait. Wind gusts up to 70 mph are expected and a small
chance to see gusts up to 75 to 80 mph. Winds will linger at St.
Lawrence Island through the middle portion of the week, however
they will be weaker with gusts up to 50 mph expected.
- With strong northerly winds we will see rapid ice growth from
the Bering Strait to St. Lawrence Island. With open water still
to the north of Savoonga there could be some small freezing
spray concerns in town. Temperatures will still be 10 to 20
degrees above 0, that will help to minimize the freezing spray
concerns.
- Eastern Norton Sound and the Y-K Delta Coastline will see
northeasterly winds of 35 to 45 mph through the weekend.
Analysis and Forecast Confidence...
A broad area of high pressure remains over Far Eastern Russia.
This will begin to move to the southwest as the low north of the
Canadian becomes more dominant. A low pressure off the coast of
Deadhorse will continue to weaken through tonight, and will get
sucked into the longwave trough as a weak wave. A conglomerate of
lows will continue to rotate into the Bering Sea from the Gulf of
Alaska.
At the surface a 968 mb low just north of Cold Bay in the Bering
Sea and a 1022 mb high in Siberia, will create a 40 mb pressure
gradient in the Bering Strait by Sunday morning. The ECMWF
ensemble standardized anomalies for surface wind speeds is around
1.5 to 2.5 standard deviations from the mean. These anomalies will
continue through Wednesday centered around St. Lawrence Island.
Looking into the snow chances for heavier snowfall next week.
There is not a lot of confidence in the timing and exact location,
but moderate confidence that there will be snow. As the arctic
trough digs down through the state, a deformation band will likely
set up. The location of the band will be determined on the speed
of the trough as well as the speed of a low coming across the
Alaska Range. At 700mb the GFS, ECMWF, and the Canadian are
bringing a trough into the interior portions of the state. This
would be accompanied with embedded lows in that trough. With
southwesterly flow being brought into the interior, there would be
sufficient moisture advection to help support higher qpf values
and then therefore higher snow totals. This event would be a
multi-day snow event. There are a lot of moving parts as our
pattern is very complex right now. Confidence should be improved
as the high pressure in the Siberia moves to the southwest.
Extended Forecast Days 4-7...
Sunday night an arctic front associated with a low pressure dig
into the Canadian will begin to strengthen. At 500 mb we will
see the longwave trough associated with that low begin to become
positively tilted. This trough will help to develop the heavy
snowfall potential from the Y-K Delta to the Yukon Flats. By
Tuesday we will have a reinforcing low come over the Alaska Range
and help to strengthen that trough. The timing of when these
features meet is very uncertain. If it`s quicker then the heaviest
band of snow will be to the south and if it`s slower then it will
be farther north. There will be heavy snowfall in the interior
next week, but the exact timing and placement is still very
uncertain. When the arctic front passes, expect cold arctic air
rush into much of the interior. The coldest spots are looking to
be west of Tanana, with lows in the 20s to 30s below.
Coastal Hazard Potential...
With Gale Force northerly winds, coastal erosion will be the
primary concern. We could see ice near the shoreline breakoff from
the main icepack and move around. Ice shoves should not be a
concern.
&&
.AFG WATCHES/WARNINGS/ADVISORIES...
AK...High Wind Warning for AKZ801.
Winter Weather Advisory for AKZ815-816-832.
High Wind Warning for AKZ820-821.
High Wind Warning for AKZ827.
PK...Heavy Freezing Spray Warning for PKZ801-807-816-817-851-854.
Small Craft Advisory for PKZ801.
Brisk Wind Advisory for PKZ802>806-810-850-852-853.
Gale Warning for PKZ811-856-857.
Brisk Wind Advisory for PKZ812-858.
Gale Warning for PKZ816-817-851-854.
&&
$$
157
FXAK67 PAJK 210023
AFDAJK
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
323 PM AKST Fri Dec 20 2024
.SHORT TERM.../ through Saturday night / Front moving north
through the panhandle this evening and tonight. Strong wind
this evening through Dixon Entrance and over Prince of Wales and
into Clarence Strait. Locally gusty winds the for POW and Southern
Inner channels and Baranof Island. There are also gusty winds to
40 mph near Skagway.
Precipitation wise rain or mixed for the south, and as the front
shears apart the central and northern panhandle are going to less
sure, will likely be more of a higher pop low QPF event. May need
to watch for freezing p-type as warm air continues to stream north
and colder below freezing temperatures may hang on over some of
the northern inner valleys.
Northern panhandle and for later Saturday and Saturday night look
like they will be on the drier side with the next big weather
front approaching the south late Saturday night.
.LONG TERM.../Sunday through Friday/...
Overview: Active weather into the mid range with a series of
strong lows and fronts moving into the AK Gulf from the south.
Expect warm temps, moderate to heavy rain, and strong gusts winds.
Model differences really show up Tuesday into Wednesday depicting
a low tracking towards Haida Gwaii making any forecast from that
point onward uncertain.
Mid level low over the Western Gulf remains in place through
Tuesday keeping that SW flow that keeps moving in the strong
surface lows. Sunday front looking good for storm force winds over
the Gulf and small craft to gale force winds over the inner
channels. Any marine travel Sunday will be difficult at best. With
the main low pulling off to the west overland wind gusts looking
to stay in the 40 to 55 mph range, but occasional gusts of 60 mph
or more not out of the question. Again there are indications of
near record high temps as the warm mid level air moves in so any
precip falling should be rain. And the 24 hour rainfall amounts
upwards of an inch to two inches should be seen Sunday and Monday
with lesser amounts Tuesday.
Mid week onward we are watching for a low tracking up from the
south over Haida Gwaii. GFS as been most aggressive with the
strength, timing, and northern track of this feature. Other
models starting to depict this feature but all much weaker. What
this means for SE AK if this low develops: dryer and bit cooler
weather to the north, windy and warmer with more moderate to
heavy precip for the south again. Beyond mid week, looks like much
of the same with multiple lows tracking in and no real indication
of any cold air or extended weather breaks.
&&
.AVIATION...Rain with the next frontal band has begun over the
southern TAF sites as of 00z. However, strong easterly flow with
the front is keeping ceilings elevated. LLWS is included for most
TAF sites as a result and has been increased based on latest NAM
model soundings. Precip and MVFR ceilings as the front tracks
through will be short-lived, likely less than 6 hours. Expect the
southern panhandle to be clear of the front around 6z and the
northern panhandle 12-14z. There is potential for LLWS to persist
beyond the front, although slightly weaker. Looking ahead to
Saturday morning, there is another break expected between frontal
bands...relatively similar to what was seen during the day Friday.
&&
.MARINE...The low pressure center and the associated frontal bands
out across the Gulf of Alaska will lead to swaths of Gale force
winds moving through the area into Saturday night. Small craft
winds will impact the inner water between north outflow in Lynn
Canal and southerly winds with the frontal bands.
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 9 PM AKST this evening for AKZ318.
Strong Wind from 6 PM this evening to midnight AKST tonight for
AKZ323.
Strong Wind until 3 PM AKST this afternoon for AKZ328.
Strong Wind until 9 PM AKST 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...Bezenek
LONG TERM....PRB
AVIATION...Ferrin
MARINE...Bezenek
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