Gale Warning 218, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
552 PM AKST Fri Feb 28 2020

.ANALYSIS AND UPPER LEVELS...
A weak upper short wave moved south across the Copper River Basin
this morning and produced a few snow showers. Subsidence with
ridging on the backside of this wave gave rise to some stratus
and patchy fog over the Copper River and near Cordova. Stratus
and fog across the Anchorage Bowl and western Kenai dissipated by
the late morning hours with most areas across Southcentral and the
SW Mainland mostly Sunny. A strong low pressure center moved just
north of the central Aleutians this afternoon with its associated
occluded front heading north across the Bering Sea. A secondary
low center is likely developing under a strong upper level jet
over the trailing frontal boundary over the North Pacific. Rain
and snow with gusty winds were evident across the Aleutian chain.

&&

.MODEL DISCUSSION...
Models are in relatively good agreement with the synoptic fields.
The challenge will be subtle changes in timing and track of the
low and front. For now will lean toward a blend of the GFS and NAM
for synoptic fields and hand edits and higher resolution NAMNEST
for local effects across Southcentral.

&&

.AVIATION...
PANC...IFR to LIFR ceiling/visibilities are expected again
overnight as stable conditions develop. Ceiling/visibilities will
see some improvement by the afternoon hours on Sat. Light winds
will persist through Sat morning before becoming north and
increasing some Sat afternoon. LLWS is a possibility beginning Sat
evening as winds above the surface become southeasterly and
strengthen.

&&

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

A strong front will approach from the southwest Saturday
afternoon. Snow will develop south to north along the Kenai at
this time, with blowing snow likely along the Sterling Highway
between Clam Gulch and Anchor Point. Similarly, blowing snow is
expected in the Portage Valley as well as Turnagain Pass. Travel
will be potentially difficult Saturday afternoon through Sunday
morning and as such, a Winter Weather Advisory has been issued for
these areas.

A Winter Weather Advisory is also in effect for the Susitna
Valley, with snow accumulations of 6 to 12+ inches expected on
Sunday. The higher end of this range is most likely in the
Talkeetna area.

Anchorage and the Matanuska Valley will see less snow overall than
the aforementioned locations, however approximately 6 inches are
likely before the associated low departs to the east on Monday
night.

The Prince William Sound area will likewise see significant
accumulations, with over a foot expected in Whittier and Valdez
through Monday night. Gusty winds will accompany the snowfall
through Thompson Pass.

The low will stall in the northern Gulf by Tuesday and snow is
likely to continue across coastal areas. However, a cooler and
drier pattern will begin to develop over the interior with
offshore flow developing as high pressure begins to build by mid-
week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Dry and cold conditions will continue tonight as high pressure
over the area slowly slides east. On Saturday a front associated
with a strong low over the Bering will push into southwest Alaska.
This will bring considerable snow and blowing snow to the area,
rapidly spreading northward during the day. Easterly winds will
also increase, becoming southerly over the Bristol Bay area
Saturday. This will likely cause a mix of precipitation types
(rain and snow), which will change back to all snow on Sunday as
cold air advection begins. On Sunday night and Monday, colder and
dryer air will push into southwest Alaska, with snow lingering
near the Aleutian and Alaska ranges due to upslope flow and a
slowly exiting trough.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A front associated with a low in the central/western Aleutians
will push northward across the Bering Sea tonight and eastward
across the eastern Aleutians and Alaska Peninsula. A much strong
low and front will move into the central and eastern Aleutians
late tonight. This low will move into the southern Bering south of
the Pribilofs Saturday morning, with the low center near the
Pribilofs Saturday evening. The low will then slide eastward
across the eastern Bering and into southwest Alaska late Saturday
night or Sunday morning. Considerable cold advection will push
southward across the eastern Bering including the Pribilofs behind
this low on Sunday, weakening Sunday night and Monday as the low
moves further inland.

&&

.MARINE (Days 3 through 5 Mon through Wed)...

Cold northerly flow returns to the Bering early next week. There
is moderate confidence that another strong low approaches the
western Aleutians by Wednesday morning.

Meanwhile over the Gulf, southwesterly gales will persist through
Monday. There is potential for embedded storm force winds. A low
in the northern Gulf Monday night will create strong outflow winds
in the usual places along the Alaska Peninsula (Gulf side) and
Kamishak Bay at least through Wednesday. Storm force gusts are
possible, especially through channeled terrain.

&&

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

There is mounting evidence for a highly progressive pattern across
the Bering and southern Mainland next week. An upper level trough
positioned over Mainland Alaska Tuesday afternoon quickly sinks
southward over the Gulf by Wednesday morning. This allows a
building upper level ridge over the Bering to move eastward
Wednesday evening. One feature that model solutions have seemed
to key in on is a stout upper level low interacting with the
ridge over the Bering around Thursday. There is still plenty of
uncertainty with this feature, but run to run consistency has
allowed for increasing confidence in an active pattern for the end
of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 121 125 145 152 155 161.
MARINE...Storm Warning 155 165 170 171 172 173 174 175 176.
         Gale Warning 119 120 125 130 131 132 138 150 160
                      177 179 180 181 185.
         Heavy Freezing Spray Warning 121 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
MARINE/LONG TERM...KO