Small Craft Advisory 306, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
528 AM AKDT Sun Apr 5 2020

.ANALYSIS AND UPPER LEVELS...

The resident upper level ridge that's been with us for several
days extends from northeast Alaska back to Kodiak Island. The
strong frontal boundary from a Bering Strait low is bringing 50
knot winds to the Kuskokwim Delta coast and 30+ knots to the lower
Kuskokwim Valley along with some light snow and rain. Gusty winds
have subsided some in Bristol Bay, but winds are still 20 to 30
knots in most locations. The strong push of long fetch
southwesterlies is pushing moisture over this ridge with clouds
all the way to the Copper River Basin. Some rain, snow, and fog
has seen its way into the Susitna Valley as well. Cold air is
streaming into the western Bering behind the front as witnessed on
satellite in the stratocumulus field.

&&

.MODEL DISCUSSION...

As the low moves ashore in northwest Alaska and its frontal
passage in southwest Alaska completes, the priority turns to the
developing low in the western Bering on Sunday night. General
agreement lies in it crossing the Alaska Peninsula somewhere
between Cold Bay and Bristol Bay Tuesday morning, from there the
spin-up of another low is being advertised in the western Gulf
and will command attention for its impact to Kodiak Island and any
potential beyond on the north Gulf coast and Prince William
Sound. Out in the western Bering it looks to be shaping up for an
active pattern on Tuesday, where again model agreements are
nowhere to be found at this point as we are seeing a bigger
pattern shift taking place.

&&

.AVIATION...

PANC...VFR conditions and gusty southerly winds will persist
through the day at terminal.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Tuesday)...
A short-wave ridge overhead of Southcentral will quickly exit
eastward this morning as a deep and cold low along the west coast
of Alaska pushes onshore. While the low will remain over northern
Alaska, a series of short-waves will cross Southcentral today
through tonight. At the same time, a surface cold front will
speed across Southcentral bringing unusually frigid air for this
time of year. 850 temperatures will drop from roughly -2 degrees C
this morning to -18 degrees C Monday morning. The biggest impact
will be widespread strong and gusty winds for portions of
Southcentral and the Gulf. As is typical with cold air moving in
from the west, the strongest winds will be over the western Gulf
and Kodiak Island. However, with low pressure to the north, some
of these winds will bend up Cook Inlet and make it all the way to
the Susitna Valley today.

The combination of the upper short-waves and persistent strong
west to southwest low level flow will lead to snow showers along
the southern to western slopes of mountains. Expect some showers
over the Susitna Valley and Copper River Valley as well, but with
little or no accumulation.

Despite the strong cold air advection, clouds and winds will keep
temperatures elevated today, but then expect a steady downward
trend over the next couple days. Winds will die down across most
of the region Monday night, so that will likely be the coldest
night.

As upper level flow remains progressive, a strong short-wave
trough will move in from the Bering on Tuesday, inducing a
moisture tap from the Pacific and leading to cyclogenesis over the
Gulf. Right now it does look like this storm will remain over the
Gulf, with little impact on Southcentral. If it tracks far enough
west, Kodiak could see some accumulating snow.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Sunday
through Tuesday night)...

The big story across Southwest this morning is falling
temperatures and increasing winds. Temps will continue to drop
this morning across all of southwest Alaska as a strong cold front
works its way inland. Bands of snow are expected to move inland
over the Kuskokwim Delta coast this morning. This snowfall,
combined with gusty onshore winds, will limit visibility at times
throughout the day today. A Winter Weather Advisory has been
issued for the Kuskokwim Delta coast north of Kipnuk, where the
worst conditions are expected. Areas farther inland may also see
deteriorating conditions as the bands of snow do have the
potential to reach inland areas, including Bethel, this afternoon.
By tonight, any lingering precipitation should taper off, however
winds will remain elevated before finally diminishing Monday
morning. The next feature to keep an eye on is a low spinning up
over the Pribilof Islands Monday morning. There is still
uncertainty regarding where this low tracks, however current
thinking is it will move eastward, nearing the Bristol Bay area by
Tuesday morning. This feature could bring precipitation to the
Alaska Peninsula for Tuesday. By Tuesday night, conditions
generally quiet down as a ridge builds over the eastern Bering.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Sunday through Tuesday night)...

Cold northerly flow returns to the Bering as a strong cold front
moves through. Scattered snow showers can be expected through the
day. An upper level low dropping down from the north will aid to
spin up a surface low over the western Bering this afternoon.
While models have consistently shown this low strengthening as it
reaches the Pribilof Islands by Monday morning, there is less
certainty regarding where this low tracks by Tuesday. Overall, an
easterly track with this low is expected, with the center arriving
somewhere near the Bristol Bay area by Monday night. The next
impact over the Bering will be a front approaching the western
Aleutians by Tuesday night.

&&

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

Bering Sea/Aleutians:

High pressure centered southeast of Adak Tuesday afternoon and low
pressure to the northwest of Savoonga will create a tight
pressure gradient across the northern Bering, where some sustained
gales are possible. Further south and west, a front will approach
the western Aleutians ahead of an incoming area of low pressure.
The center of high pressure then moves to Dutch Harbor on
Wednesday and into western Alaska for Thursday. This allows the
front to trek eastward into the central Aleutians and Bering, with
sustained gales possibly developing.

Gulf of Alaska:

A strengthening area of low pressure approaches the Gulf Tuesday evening,
with a sustained gale force front preceding its arrival. As this
low deepens further across the northern Gulf Wednesday morning,
high-end sustained gales, with storm force gusts, are anticipated
to develop. This low then moves ashore between Cordova and Yakutat
Wednesday evening, with sustained gales continuing near the
northern Gulf Coast. An offshore flow pattern develops on Thursday.

&&

.LONG TERM FORECAST (Days 3 through 7/Wednesday through Saturday)...

Guidance is in fairly good agreement leading to high confidence on
the long term upper-level pattern for Wednesday and Thursday with
an upper level trough over the mainland and a modest upper level
ridge over the Bering. This will lead to cold temperatures over
the mainland of Alaska with warmer temperatures over the Bering
and Aleutian Chain. The upper level ridge over the Bering will
slowly work towards the mainland Thursday leading to a warming
trend. Beyond Thursday night is when the models begin to diverge
on the upper level pattern and the placement of features. While
the trend is there on both models for a warming trend, the degree
to how strong this warming trend will be is still uncertain. This
is leading to only low to moderate confidence in the forecast for
temperatures Friday into Saturday of next week. The placement of
features in the upper level flow is in question as one model has
the upper level ridge further west and more amplified while
another is less amplified.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155.
MARINE...Gale 119 120 125 130 131 132 137 138 139 141 179 180 181 185
              351 352.
         Heavy Freezing Spray 180 181 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...LTB
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...PD/MV