Gale Warning 168, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
424 PM AKST Mon Feb 10 2020

.ANALYSIS AND UPPER LEVELS...

Satellite shows mostly clear skies over the mainland today as
high pressure builds in the wake of the low in the the Gulf of
Alaska. Westward, over the Aleutians and Bering Sea, a strong
front extends its way toward the parent low southwest of Shemya.
Winds along this front have diminished overnight, but are still
gusting to gale force through the central Bering Sea and over the
Aleutians. The high pressure building in over the mainland is also
dropping temperatures across the entire area, with the majority of
the western mainland at 0F or below. In the Southcentral area, the
combination of the retreating low and the building high is
beginning to cause outflow winds in the usual areas, but so far
these winds have remained below 30 mph so far, with a few
exceptions in exposed terrain.

&&

.MODEL DISCUSSION...

Models continue to be in good agreement through the short term
with the next inconsistencies appearing Wednesday in the north
Pacific with the low developing south of the chain. The main
significance of these differences will result in whether Kodiak
City sees snow or a wintry mix on Wednesday as the low moves
nearly overhead. The 18Z NAM indicates a trend toward the further
westward GFS solution, indicating higher confidence in mixed
precipitation for Kodiak City.

&&

.AVIATION...

PANC...VFR conditions will persist. Northerly winds around 10 kts
are expected to remain through the TAF package.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Thursday)...

After a significant delay, cold air has finally arrived across
much of Southcentral this afternoon. Along with the cold air have
been clearing skies, though some lingering stratus has persisted
primarily over the Copper River Basin and the eastern Matanuska
Valley. Those clouds have been eroding so the clear skies should
eventually reach those areas as well over the next few hours.
Tonight's highlights will be a brief return to below normal
temperatures, as many areas drop below zero from East Anchorage,
the Matanuska Valley, and the Copper River Basin. Single digits
above zero are expected for West Anchorage, and much of the
western Kenai Peninsula. Along the coast where the winds will stay
higher, temperatures will hold in the teens and 20s.

Tuesday will start off as another sunny day for most of
Southcentral, and temperatures for most areas will stay in the
teens for highs. Clouds will increase from the south through the
afternoon as the next low approaches the area. Aside from Kodiak
Island, all areas should reach sunset precipitation-free. The low
advertised in previous discussions to move into the Gulf Tuesday
night remains on track. However, there was a very notable change
from yesterday, in that the low is significantly further west, and
now looks to track along the coast of the Alaska Peninsula through
Tuesday night, then turn east up along the east coast of Kodiak
Island Wednesday morning, then depart quickly towards the eastern
Gulf by late in the day Wednesday. Along this track, the leading
warm front is expected to move north past Kodiak Island and into
the northern Gulf by Wednesday afternoon. The warm front, in
addition to bringing warm air, will keep the winds easterly
over Kodiak Island Tuesday night ahead of the front. The easterly
winds will not have any cold air to work with, as they will warm
up after traversing the upper 30s waters of the Gulf. Therefore,
the threat for hazardous snow in Kodiak has dramatically
decreased since 24 hours ago. That isn't to say that there won't
be any snow. In fact, the snow may come down heavily for a time
Tuesday night. However, temperatures should at worst only cool to
the freezing mark, and will likely stay a few degrees above
freezing through the entire event. Thus, any snow, which may mix
with rain, will melt at the ground. It will certainly be windy as
well, so blowing snow will be a concern, but the snow will be a
heavy, wet snow, so resuspension is not expected.

The front is expected to stall out along the coast into Wednesday
morning. Some moisture should try to make it north, especially
across the Copper River Basin, where a few inches are possible.
For Anchorage, the Mat Valley, and the western Kenai, however,
flurries are about all we are going to see during the morning
commute Wednesday morning. During the day, the low rapidly moves
off to the east, with skies gradually clearing Wednesday night.
Thursday should be another quiet day for most, though the gap
winds will persist.

&&

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

An elongated warm front associated with a low roughly 200 miles
southwest of Attu continues pushing northward through the Bering
Sea, with general warm south flow behind the front. This will
cause the Arctic air spreading from the Interior to recede
slightly. Expect a slight warm- up over the Southwest Mainland
Tuesday, though surface winds should remain northeasterly. A
secondary low will form south of the AKPEN Tuesday, at the triple
point. Snow is likely along the AKPEN into the Bristol Bay area
and the Alaska Range Wednesday... possibly spreading into the
middle Kuskokwim Valley. The precipitation forecast in the
Kuskokwim Delta will be a challenge. The cold, dense air in place
will provide a good lifting mechanism, and models show some
indication of a shortwave or two ejecting northward from the
triple point low. Much will depend on the speed with which the
low exits the area, as any precip will have to overcome dry air in
the low levels. As the low exits eastward to the Gulf late
Wednesday into Thursday, cold dry conditions will return to the
entire Southwest Mainland.

&&

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

A vertically stacked low centered roughly 200 miles southwest of
Attu continues to bring gales to the western Bering, and along the
leading front as it pushes northeastward. A secondary low can be
seen developing on satellite roughly 200 miles south of Kiska. As
this tracks northeast toward the Chain, expect enhanced
precipitation from the eastern Aleutians and AKPEN north. Expect
visibility impacts from blowing snow in the Pribilofs Tuesday.
For the most part, winds will gradually decrease Tuesday into
Wednesday. A wave roughly 500 miles east of Hokkaido (Japan) will
develop into a storm force low approaching the western Aleutians
late Wednesday into Thursday. The associated front will bring a
period of storm force easterlies to the western Aleutians, and a
broad swath of gales to the Bering Sea. There is some uncertainty
as to whether storm force winds will make it into the Bering...
models differ with how far north the low bottoms out. In any case,
this low will bring a return to active weather.

&&

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

A strong storm will be moving across the central Aleutians into
the central Bering Sea Thursday and Friday then weaken Sunday.
Gale force wind can be expected north of the low and in advance of
it's front Thursday and Friday. Gale force west and southwest wind
is likely south of this low as it crosses the Aleutians Friday.

Over the Gulf of Alaska, winds will remain below gale force
Thursday through Saturday.

&&

.LONG TERM FORECAST (Days 3 through 7: Thursday through Monday)...

A strong ~960mb storm crosses the central Aleutians Thursday,
moving into the central Bering Sea as it weakens. This storm will
push a front through the Aleutians and Alaska Peninsula that will
then elongate to the east as a triple point low forms along it
near Kodiak Thursday night. The main low over the Bering Sea will
gradually weaken through Friday and Saturday. The models diverge
on the location of the center Friday and Saturday and also begin
to diverge significantly Saturday night and Sunday with respect to
the remnants of this storm and the approach of the next strong
Aleutian and Bering Sea storm Sunday. The latest model runs
support a much stronger storm than the previous solutions, but
also diverge on the location of the storm center. Confidence in
the extended forecast beyond Saturday is low due to the varied and
significantly differing solutions. The approach will be to
maintain the current forecast solutions with adjustments trending
toward the ECMWF solution.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 119 120 130-132 138 139 150 155 170 172 173-175
177-179 185 351 352 411-414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...LF
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...SA