Gale Warning 173, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 AM AKST Wed Feb 12 2020

.ANALYSIS AND UPPER LEVELS...

There is a mature system with a front that spans from Southcentral
to the North Pacific. The occlusion was over the Alaska Peninsula
early this morning. There is a developing low south of the Western
Aleutians. Gales have been detected with both systems using ASCAT
(advanced scatterometer) data. There is a 130+ knot jet core south
of Kodiak and a 160+ knot jet core south of the Western Aleutians.
Lightning strikes were detected early this morning with the system
south of the Western Aleutians. The radars at King Salmon (PAKC),
Kenai (PAHG) and Middleton Island (PAIH) have all been active
this morning.

&&

.MODEL DISCUSSION...

For initialization purposes compared the 9z radars at Kenai and
Middleton Island to the QPF at 9z on the models
(GFS/NAM/ECMWF/Canadian/HRRR). The HRRR, Canadian and the ECMWF
were the only models that had precipitation near Hope at 9z while
the GFS and NAM were bone dry. Meanwhile on the Middleton Island
radar there were some minor differences with the precipitation
band near Valdez but all 5 models did reasonably well over the
northern Gulf Of Alaska. The GFS ensemble members are tightly
grouped through 60 hrs. The GFS ensemble mean is in lock step with
the operational run of the ECMWF in the Bering and the North
Pacific through F60. Temperatures in the boundary layer associated
with the low continue to show some variance even in the first 24
hrs of the forecast package. The models all show warm air
advecting into Southwest and nudging the arctic air mass eastward.

&&

.AVIATION...

PANC...Active TAF package. Low ceilings will persist as the
frontal boundary moves inland. At 11z Wednesday the cig at PANC
was 4,400 ft which rapidly deteriorated to 1,200 ft by 13z. Snow
has fallen on the tarmac this morning and more is expected this
morning. The visibility was reduced to 1 sm at 13z. Degraded vsby
anticipated as the precipitation moves through. The models show
moisture getting wrapped around the back side of this low and near
the aerodrome until 9z Thursday and VFR conditions may not return
until after that.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The low in the Gulf will slide eastward today. There is plenty of
moisture with this low and snow is spreading inland, especially
over the Copper River Basin. Winds will be fairly gusty over the
Kenai Peninsula, with some areas of blowing snow. The strongest
winds will be from Portage through Turnagain Pass, and along Cook
Inlet. Conditions will slowly dry out from west to east tonight
through Thursday as the low pushes into Canada. Offshore winds and
cold advection will return to the area as a sharp ridge builds
over the area. Most of Southcentral will be cold and dry Thursday
and Thursday night. For Kodiak, another system will push into the
Island Thursday night bringing snow, but winds will be lighter
than they were last night (Tuesday night).

&&

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

Northeasterly winds have developed over much of southwest Alaska
as anticipated, with the southern Bristol Bay area continues to
see snow and blowing snow. Snow and blowing snow exists in
southern Bristol Bay and along the Alaska Range due to a decaying
front that remains nearly stationary. Its parent low (that moved
through the eastern aleutians yesterday) is still moving east into
the Gulf of Alaska. After this low exits later today the front
will become a non factor. However, it does look like weather will
linger a little longer than expected, so extended blowing snow
along the AKPEN through this afternoon.

Northeasterly winds will continue through the day today and
slowly diminish overnight tonight. This flow is still expected to
usher in colder temperatures and wind chills pushing -45F. As a
result issued wind chill advisory starting midnight. Dropped
temperatures a few degrees tonight for interior southwest AK with
cold air barreling from the interior. Winds also look to stay
elevated coming down the Kuskokwim River Valley tonight and
tomorrow, so reflected this in the forecast. Be advised it will
be cold for the next few days.

&&

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

The weather story for the Bering continues to the be storm force
low pressure system that will move north through the
Bering and will enter our forecast area later today. This storm
is rapidly deepening as it approaches. It is now close enough to
our forecast area that is can be seen on satellite and so far it
appears to be on track. The latest model runs have the storm
taking a bit more of an easterly track, so adjusted the storm
track slightly tonight. This storm is also sizable and will
encompass much of the Bering Sea. Therefore, even with an
adjustment to storm track, many locations will still see at least
gale force winds.

Also of note this morning, a stretched out decaying front is still
sitting over the eastern Bering/Aleutians and providing some snow
showers and elevated winds with blowing snow. This front will be
a non-factor after today.

&&

.MARINE (Days 3 through 5)...

Bering/Aleutians: A gale force low in the central Bering will
weaken Friday into Saturday. Another strong low will approach the
western Aleutians late Sunday, likely bringing another round of
gales.

Gulf of Alaska: Winds will generally remain below gale force
through Sunday. However, model agreement is poor so confidence in
the forecast is below normal.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Beginning the extended period forecast on Thursday afternoon,
there will be a large and deep upper level cyclone with a stacked
surface low over the Western Aleutians with the occluded front
moving into the eastern Bering Sea. Cold northwest offshore flow
will be keeping the mainland dry at this time. As the front shifts
east, the zonal flow will result in a developing triple point low
around Kodiak Island. Snow will move into the AKPEN and parts of
interior Bristol Bay, but this will not make much northward
progress as the arctic high will be in place, so much of the
energy will move into the Gulf of Alaska and fall apart as it
moves east Friday. This pattern means most of Southern Alaska will
remain drier and colder, although Southwest Ak will be open to
brief bouts of clouds and snow through the weekend as the Alaska
Range will keep Southcentral much drier given the fast westerly
flow aloft.

The upper level flow reamplifies sometime Sunday night, and this
will likely bring in more stormy weather for the Southern
Mainland, with a myriad of impacts including inland snow and
stormy seas. It looks to get colder thereafter as another arctic
trough digs in.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 155. WSW Blowing Snow 121 125. WSW
Snow 141.
MARINE...Storm 119 130 132 138 411 413 178 177 176 175 174.
Gale 352 120 131 139 414 412 150 155 170 171 172 173 179 180 185.
Heavy Freezing Spray 139 414 412 150 160 165 185 150 160 165 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BJB
MARINE/LONG TERM...MM