Winter Weather Advisory 37, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
543 AM AKDT Wed Apr 7 2021

.ANALYSIS AND UPPER LEVELS...

An amplified upper-level ridge advances through Southwest Alaska
followed by an upper low from the Bering Sea today. A relatively
active weather pattern remains over the region, essentially
inviting hazardous blizzard conditions through Kuskokwim Delta
and blowing snow through Bristol Bay this morning. A shortwave
embedded along the zonal flow of the upper-level low will mainly
focused on eastern Bering and Southwest Alaska today.

Satellite and weather observations indicate steady light to
moderate rain and areas of patchy fog over Pribilof Islands, and
warm temperatures over the Aleutians in response to a warm front
hovering over the central Bering. Over the Gulf of Alaska, warm
southwest winds combined with warm temperatures in the lower 40s
to lower 50s resulted in steady light rain over Kodiak Island.
Meanwhile, clear skies and colder temperatures surround much of
Southcentral and Kenai Peninsula this morning.

&&

.MODEL DISCUSSION...

Model solutions are in favorable synoptic agreement through
Friday. A set of expected lows and frontal systems over the
Bering are nicely paced eastward across the Gulf of Alaska in the
next couple days. Long-term models start to deviate the placement
of the next Bering low by Friday night, but its frontal axis
seems to be handled quite well by the models.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds will continue.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Today through Friday Night)...

Radiational cooling and clear skies has allowed overnight lows to
drop down anywhere in the single digits to the teens in the low-
lying areas and surrounding high elevations. A low-level ridge of
high pressure will move eastward over the Southern Mainland and
help relax the northerly winds blowing across the usual gaps and
passes, including Seward, Whittier, Valdez, and the Copper River
Delta. Attention immediately turns to a late-season storm event
that will make an impact to the area starting later today. A
potent upper-level low from the Northern Bering will dive
southeastward over the southern AKPEN, with a triple point low
developing along a frontal boundary near the Western Gulf. An
initial push of warmer air ahead of the low will bring rain to
Kodiak Island on Wednesday night, and then transition to all snow
early Thursday morning with wrap around moisture on the backside
of the low as it lifts northward. Moreover, a 700-500 mb moist,
southwesterly flow aloft will bring snow into the Cook Inlet,
Anchorage Bowl, and Mat-Su Valleys this evening. As the low moves
over the Central Gulf on Thursday morning, a cross barrier jet
will form along the North Gulf Coast, inducing a downsloping
effect. With limited moisture reaching in these aforementioned
areas, current thinking is to keep small chances of snow, with the
rest of the snowfall accumulations concentrated on the Anchorage
Hillside, the coastal areas of Prince William Sound, and the east
facing mountain slopes as well. Moist, cyclonic flow will keep the
chances of scattered snow showers over the Copper River Basin as
well as north and west facing mountain slopes through Friday
afternoon as the low exits to the eastern Gulf.

Thereafter, a polar shortwave trough will move south from the
northern half of the state on the heels of the aforementioned Gulf
low late Thursday night and into Friday. Some minor differences
with the latest model solutions has to do with how far south does
the polar low go and stays in lockstep with the exiting Gulf low.
Regardless, with 850 mb temps dropping between -20C and -30C by
Friday morning, there is a very high likelihood of gusty,
northerly winds will occur as very cold, arctic air spills across
the Southern Mainland. In addition to the winds funneling through
the usual gaps and passes, Anchorage Bowl may potentially reach up
to 45 mph or more by Thursday night. Heavy freezing spray will
also be a major concern for the Barren Islands, Kamishak Bay, and
Shelikof Strait as strong, northwesterly storm to hurricane force
winds will blow across the usual gaps and passes Thursday
afternoon into Friday morning (please see Marine Weather Statement
for details).

Wind chills be another area of concern associated with the strong
winds and colder temperatures. Winds are expected to diminish by
Friday night into Saturday morning, allowing overnight lows to
plummet anywhere in the single digits to sub-zero. Some of these
overnight lows will have the potential to approach or break daily
cold temperature records for early to mid April. With little
recovery in sight, expect temperatures to remain below normal for
this time of season. Winter-like weather will hold firmly over us
for a little while longer.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Today through Friday)...

A front is currently approaching the Kuskokwim Delta coast and is
expected to bring prolonged blizzard conditions to this area.
Easterly winds will gradually back to northerlies and become
stronger through the day, gusting up to 55 mph by this evening. As
such, even after the snow ends, visibilities of one quarter mile
remain likely through Thursday morning. Snow will also track from
west to east across Bristol Bay over this time period. Blizzard
conditions are briefly possible along the coast between Cape
Constantine and Goodnews Bay this morning. Overall, winds will be
weaker south of the low, however snow and blowing snow will
persist overnight into Thursday with up to 8 inches possible over
interior regions near Iliamna. Skies will clear Thursday and
Friday, however extremely cold temperatures are expected with
lows well below zero on Friday morning across the entire region.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Today through Friday)...

A low tracking across the eastern Bering will strong winds to the
Pribilofs this evening as well as moderate precipitation to the
eastern Aleutians and Alaska Peninsula. Strong cold advection will
lead near hurricane force wind gusts developing in northwesterly
winds on the south side of the Alaska Peninsula by Thursday
morning. These diminish from west to east into Friday. An
occluding front will move across the Aleutians through Friday.
Precipitation will likely remain all rain, with snow developing
on the backside of the associated low over the western Aleutians
on Friday evening.

&&

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

A very active weather pattern is expected through the weekend with
high confidence to start. Friday, a low in the northeastern Gulf
will maintain gale to storm force winds, especially through bays
and passes across Shelikof Strait and towards Kodiak before
beginning to dissipate Friday afternoon. A low just to the west of
Shemya will keep gale to storm force winds along its front across
the central Bering. As it dissipates into Saturday and moves
north, winds and waves will die down.

After this, confidence breaks down with models in stark
disagreement on the placement of a front across the Gulf or the
formation of a low. At best expect small craft winds and waves
across the Gulf, at worst expect gale force winds and waves
through Sunday. For the Bering, there are also discrepancies on
the placement, strength and track of an area of low pressure. At
worst expect gale to storm force winds across the Aleutians and
at best expect small craft winds and waves through Sunday. How
long the increase in winds and waves associated with this low will
last has yet to be determined.

&&

.Long Term Forecast (Days 4 through 7: Saturday through Tuesday)...

Beginning Saturday, model solutions diverge with forecast confidence
being on the low end. There is some agreement with the location
of a front bringing precipitation and higher winds across the
eastern Bering and coastal locations of the Southwest beginning
Saturday morning. Precipitation is also anticipated across the
remainder of the Bering and the Aleutians with an area of low
pressure located somewhere in the western Bering. The amount of
precipitation and strength of the wind will vary depending on
which model solution plays out. This feature looks to propagate
into Southcentral on Sunday, with the same anticipated results of
precipitation and higher winds. The same issues continue with this
forecast as far as how much precipitation and how high the winds
will be, with further discontinuity in the location and strength
of this front. It does look as if precipitation could largely be
isolated to the coastal regions and higher elevations of the
northern Gulf through Monday, with downsloping possible for the
Anchorage Bowl. Precipitation seems to vary across the Bering and
the Southwest due to the low in the Bering and its track, strength
and placement from Saturday through Tuesday. All in all, expect
an active weather pattern for the long term, with the finer
details being worked out as models come into better alignment.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155. Winter Weather Advisory 161.
MARINE...Hurricane Force Wind Warning 130
		 Storm Warning 119 131 132 138 150 352
         Gale Warning 120 121 125 127 136 137 139 155 160 165
					  170 172 175 177 178 179 180 181 185 351
					  411 412 413 414
		 Heavy Freezing Spray 130 131 138 139 140 160 180 181 185
							  414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CMB
SOUTHCENTRAL ALASKA...MF/TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...CK