Heavy Freezing Spray Warning 124, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 PM AKDT Thu Mar 18 2021

.ANALYSIS AND UPPER LEVELS...

A surface low and associated shortwave trough has setup over the
Mainland and extends to the North Pacific with an embedded 100
knot jet streak from Southwest AK to the central Gulf. Middleton
Radar is detecting snow showers associated with the surface low
near the coastal areas of Prince William Sound (PWS) northward
into the Copper River Basin. Additionally, wrap around moisture
around the low coupled with upper level support has contributed
to some light snow since early this morning from the western
Kenai Peninsula to the Anchorage Bowl. The snow is tapering off
this afternoon due to a combination of drier air aloft and the low
slowly exiting east of PWS. The 12Z ANC sounding had drier air at
the surface with a warm nose just above the surface, and a moist
layer in the mid levels with increasing westerly winds aloft.

Further west, a front associated with the stationary upper level
low over the northern Bering is tracking east and is expected to
reach the Pribilofs this evening. Meanwhile, another surface low
and associated baroclinic front over the North Pacific is forming
in the left exit region of a 140 knot jet streak and moving
toward the western Aleutians near Shemya. In between the trough
over Gulf and northern Bering, a ridge of high pressure is
building over the central and eastern Bering, leaving partial
clear skies over Southwest AK.

&&

.MODEL DISCUSSION...

Models are in good agreement with the synoptic scale features in
the short term and still on track for a progressive pattern over
the Bering/Aleutians through the weekend. Additionally, model
solutions are in a consensus with a triple point low forming along
a frontal boundary near the western Gulf and Kodiak late Friday
night. However, models deviate on the exact track of the front
over Kodiak and how much precipitation, if any, makes its way
toward Southcentral for this weekend.

&&

.AVIATION...

PANC...Expect VFR conditions for the rest of today into this
weekend. A period of winds with gusts to 15 mph are possible this
afternoon, diminishing by sunset. Light winds are then expected
tonight through Friday morning.

&&

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

An upper level low and associated weak surface low will continue
to move off to the southeast towards Southeast Alaska this
evening. Any lingering light snow, mainly south of Glennallen, is
expected to end later this evening. Some light snow was still
ongoing in Eureka which is expected to taper off and end later
this evening as well. For the remainder of Southcentral, dry
conditions but cold temperatures will continue through the weekend
with an increase in some mid to upper level clouds across the
area on Saturday. This will continue the streak of below normal
temperatures as we continue to head for the longest streak of
below freezing in Anchorage since record keeping began. Stay tuned
to see if we indeed set the record later this month! Also,
expect the normal winds out of gaps and passes as an offshore flow
regime continues tonight and into the weekend.

Lastly, the next storm system is expected to move from the Bering
into the western Gulf of Alaska beginning Friday evening. There
still remains uncertainty for this system especially in terms of
how much warm air will make it into the Kodiak City area.
Initially, precipitation will start out as snow Friday night, but
there remains discrepancies as to how much warm air will make it
into the area. One piece of guidance shows a stronger and closed
off low that moves relatively close to the Kodiak area. If this
were to occur, then enough warm air would be able to wrap around
the low and be brought into the area to change snow to rain
Saturday morning. Rain would then be the predominant precipitation
type through Saturday afternoon/evening before the low starts to
pull away to change rain back to snow. Most of the other guidance
is showing a more elongated surface low which will limit the
amount of warm air that is able to make into Kodiak. With the
March sun and these differences in the model guidance, a very
tough forecast is in play for Kodiak. For now, think this could be
a sizable event as when looking at the thicknesses also most are
below the 1300m mark with 1300m being the delineation line for
rain versus snow with 1290m being more a rain/snow mix. One other
item to note is the forecasted high temperatures for the area in
the mid to upper 30s. Even if it stays all snow it is likely to be
of a heavy wet snow variety. Highly recommend checking back for
the latest forecast updates as this is potentially a high-bust
forecast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Saturday)...

Generally clear and calm conditions are expected through the
evening tonight as an upper level ridge gradually moves eastward.
Increasing cloud cover is expected across the area tomorrow, as
an approaching front reaches the coast by late afternoon. Snow
will spread in across the Bristol Bay area Friday night through
Saturday morning. A few inches of snowfall is expected, with the
greatest totals likely along the coast. As the bulk of the upper
level energy shifts eastward, colder air will fill in on the
backside and lingering snow showers are likely across the area
through the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Saturday)...

A gale force low centered over the northern Bering is pushing a
front across the central Bering this evening. Snow and blowing
snow has arrived over the Pribilofs, and will continue this
evening. As the front moves through, temperatures are expected to
increase with warm southerly flow and precipitation will
eventually change to rain by early Friday morning. With a broad
upper level trough in place over the Bering through the weekend,
scattered snow showers will persist. By Sunday, an upper level
trough arrives over the northern Bering, reinforcing colder
northerly flow and showers across the western Bering.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

Gulf: A low exits the Southeast Gulf late Mon. A new low and
front moves to the Central Gulf for Tue. Small craft winds spread
from the Shumagin Islands to the Barren Islands and into the Gulf
for Tue.

Bering: A low and front move into Western Alaska for Sun. Mon and
Tue should bring gale force winds over the Aleutians. A new low
and front moves into the Western Bering by Tue. Widespread high
end southerly gale force winds extend into the Central Bering for
Tue. Seas building to 22 feet spread into the Central Bering by
Tue.

&&

.LONG TERM FORECAST (Days 4 through 7)...

The long term forecast begins late Sunday with an upper-level
ridge extending from Pribilofs to the North Slope. This feature is
bookended by two upper-level lows, one over the Al-Can boarder
and the other over the Gulf of Anadyr. This is resulting in an
omega block type pattern for the northern half of the state, while
a more zonal flow dominates across the Aleutians and Gulf. The
Gulf of Anadyr low slides to the northeast on Monday, bringing
snow to the western coast. The track of this low not only allows
the upper-level ridge to retreat, but also begins the transition
to a more zonal pattern from the Bering east across the state by
mid-week. This pattern shift will bring a strong low into the
western Bering with a front moving quickly east across the Bering,
reaching the western coast by late Tuesday. As the front moves
onshore and weakens, a second shortwave will move from the North
Pacific northeast toward Southwest Alaska. This feature looks to
deepen a secondary low as it tracks into the Y-K Delta Wednesday.
Its associated front moves over Southcentral with a triple-point
low likely spinning up in the northern Gulf. The uncertainty for
Southcentral will be how much warmer air moves in along with the
southwesterly flow ahead of the developing Gulf low. This current
set up could bring a brief period of warmer temps and mixed
precipitation across the Kenai Peninsula and Anchorage Bowl
before the Gulf low deepens, moves east, and wraps colder air
back over the Southern Mainland.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 120 121 130 131 138 179-185.
		 Heavy Freezing Spray 121 129 130 139 160 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...MF