Heavy Freezing Spray Warning 42, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
353 PM AKST Sat Feb 20 2021

.ANALYSIS AND UPPER LEVELS...

The weather setup today is high pressure and very cold temperatures
over mainland AK, while low pressure and unsettled weather exists
in the Gulf of Alaska and the Aleutian Islands. Satellite shows a
broad, elongated area of low pressure stretching from near Kodiak
northeast across the Gulf. This low is providing continued light
snow for Kodiak Island. This low is also pushing a band of mid-
level cloud cover into Southcentral AK. A more compact low is
spinning slowly east across the Aleutians, bringing a mix of rain
and snow to that area. Interestingly on satellite, the very cold
temperatures associated with high pressure over mainland AK are
depicted on Infrared. These surface temperatures are showing up
because they meet the temperature threshold normally reserved for
cold cloud tops (what we normally use IR to look at) but in this
case surface temperatures are cold enough to show as well. Clearly,
winter is still firmly entrenched.

&&

.MODEL DISCUSSION...

Models are doing well overall in the short term. This latest run
shows models to be handling the low near Kodiak better. However,
there remains some disagreement on how far north precipitation
will reach as this low tracks across the Gulf. Right now, light
snow along the immediate coastline of Southcentral AK looks like
a safe bet. Beyond that, models are locked on well to the weather
so confidence is high for the short term.

&&

.AVIATION...

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Saturday
Afternoon through Tuesday)...

A weakening front is currently pushing inland bringing mainly
clouds. However, some light snow will fall across the Kenai
Peninsula towards Prince William Sound with a light dusting of
snow in a few lower elevation areas. A low and frontal system
currently moving east of Kodiak Island will track northeast near
Yakutat by early Sunday morning and weaken. This will bring light
snow to Kodiak Island through this evening with another inch or
so ending before midnight, while light rain and snow may fall near
Cordova tonight. As this low pushes east outflow winds will
increase tonight and continue through Monday. These stronger
winds will continue to cause periods of heavy freezing spray over
parts of Cook Inlet and the Barren Islands. Otherwise, cold
temperatures will continue across most of Southcentral north of
the coast, with single digits to below zero temperatures.

Sunday into Monday the moisture from the front will bring some
light snow to the Copper River Basin with 1 to 4 inches of light
snow possible through Monday.

Sunday night and Monday a shortwave trough will swing out of
Southwestern Alaska. This will bring a chance of snow from Homer
northward towards Anchorage with a dusting of snow possible.
Worst case near an inch of snow could fall, however with the dry
atmosphere think it is most likely to be a dusting. There could be
some blowing snow early Monday morning around the Homer Bluff.

Monday night and Tuesday a ridge will pass across the area with
drier conditions before another low pressure system enters the
Gulf late Tuesday and Wednesday with a more active pattern ahead
by the middle of next week for Southcentral.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 3: This
afternoon through Tuesday evening)...

Light snow is expected to continue for eastern Bristol Bay (i.e.
King Salmon, Egegik, Iliamna, Igiugig, and Dillingham) through
this evening. Light snow will then taper off to flurries and end
from west to east. Areas furthest east will still have some
flakes into the early morning on Sunday due to some upslope
against the Alaska Range as the upper level trough lifts through.
Generally up to 1 inch is expected for many of these areas through
early morning Sunday with just a coating to as much as a few
tenths of an inch near Dillingham.

The remainder of Southwest will remain quiet but will turn even
colder for tonight through Monday evening. One potent upper level
shortwave will move through tonight with another one for Sunday
night which will bring in reinforcing shots of arctic air.
Temperatures across the Kuskokwim Delta and Kuskokwim Valley are
expected to be in the negative teens to negative 20s below zero
both tonight and Sunday night. With the winds being generally
light and under 5-10 mph, wind chills will be around 30 to 35
degrees below zero with a couple readings maybe as low as 37 or 38
degrees below zero but don't think these will reach the Wind
Chill Advisory criteria. As a result, the Wind Chill Advisory was
cancelled for tonight, especially because of the diminishing
winds and criteria wasn't met last night.

Lastly, the next big weather system will be a front moving towards
the area from the Bering Sea Monday evening. This front is
expected to bring a widespread snowfall to much of Southwest as
the arctic high retreats back to the north. There may be some
areas of blowing snow mainly for Nunivak Island and the immediate
Kuskokwim Delta coastline (i.e. Kipnuk and Toksook Bay to Hooper
Bay). However, this is expected to be relatively brief Monday
evening into early Tuesday especially as the front will be
weakening as it approaches the coastline. Right now, it appears
that this front will bring a fairly substantial snowfall to the
Kuskokwim Delta Monday evening through Tuesday with the potential
for a heavy accumulation (in excess of 6 inches). One other thing
to mention is that this is expected to be a somewhat long
duration event leading to the 6 inch accumulation over greater
than 12 hours. Elsewhere across Southwest looks to be a general 3
to 6 inch event.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3: This
afternoon through Tuesday evening)...

An active weather pattern is expected to continue for the Bering
Sea for the duration of the forecast period as a broad upper
level low remains in place. A storm system currently positioned
just north of Adak will continue moving off to the east and into
the North Pacific east of Dutch Harbor Sunday afternoon. Latest
ASCAT data showed gale force winds mainly on the Pacific side of
the Aleutian Island Chain. Therefore, the winds were updated to
reflect this low as it was stronger than projected yesterday.
Mainly expect a mix of rain and snow along the Aleutian Chain as
this system moves through.

Also, expect heavy freezing spray near the ice edge to continue
through the forecast period as the same general pattern remains in
place.

Lastly, another potent gale force storm system will move into the
western Aleutian Island Chain beginning Sunday afternoon. This
system is expected to traverse the Bering and the Aleutian Island
Chain the remainder of the forecast period bringing mainly rain to
much of the eastern Aleutians due to the warm air that will be
brought north with the system. The Pribilofs will be closer to
where enough cold air may hang on to keep it all snow but some
rain may mix for a time especially Monday afternoon.

&&

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

Bering Sea: A low continues to track into the Eastern Bering by
Thu. Models agree, so confidence is good. Widespread small craft
winds and waves wrap the low through Thu. Wave heights to 21 feet
on the Pacific side, 16 feet in the Eastern Bering, subsiding
through Thu. A new low and front enters the Western Bering late
Tue and moves to the Central Bering by Thu. Widespread high end
small craft winds with areas of gale force winds wrap this low
through Thu. Wave heights to 33 feet on the Pacific side, 23 feet
on the Bering side through Thu.

Gulf of Alaska: A well developed low and front move over the Gulf
for Wed and Thu. Models vary, but confidence is good. Widespread
high end small craft winds and waves with areas of high end gale
force winds wrap the low through Thu. Wave heights building to 20
feet for Thu.

&&

.LONG TERM FORECAST (Days 4 through 7/Wednesday through Saturday)...

The long-term looks to be active, with the upper level synoptic
flow showing a more zonal pattern for our forecast area. A series
of troughs and ridges move through until a deeper longwave trough
sets up of the Bering late in the week. A ridge also sets up over
mainland AK ahead of it. Models differ on the placement and
strength of both, but all are in agreement that this general
pattern sets up.

On the surface, we start out midweek with a low somewhere in the
Eastern Bering and a low somewhere near the Southwest Gulf. Models
have a pretty big spread on where both setup, so low confidence on
the specifics of the forecast in the long-term. Moving through
the period, a series of weak lows look to exist in the Bering and
a low moves through the Gulf. The mainland looks quiet. Beyond
that, we can't discern much. Overall, moderate confidence in the
weather pattern. We know it will be active but that's about it for
now.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119 120 130 131 139 150 172 174 176 178.
 Heavy Freezing Spray Warning 127 130 131 139 160 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BB
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...MK/BB