Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 191303
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
403 AM AKST Fri Jan 19 2018

.ANALYSIS AND UPPER LEVELS...
There are 2 main features across Alaska today. The first is a
decaying low over the Gulf of Alaska which continues to produce
showers that are detectable on the Middleton Island radar. A
another low south of the aforementioned low continues to push
eastward along 50N which will not directly impact South Central
but it will interact with the remnants of the low just outside
Prince William Sound. The other primary feature is a
strengthening surface high near the Gulf of Anadyr. This surface
high has been over Siberia will continue to migrate towards the
Central Bering. Anomalously cold air is trapped in this feature
and this will have a major impact on the region as the forecast
period unfolds.

&&

.MODEL DISCUSSION...
There is good model consensus with the synoptic features and
good run to run continuity. That said, there are a few areas of
uncertainty regarding timing of fog dissipation and pinpointing
the temperatures as we head into a much cooler pattern.

&&

.AVIATION...
PANC...Fog has moved down Knik Arm and has reduced visibility and
cigs. The latest VIIRS image has a large area of stratus spanning
from Knik Arm and down Cook Inlet which is camouflaging the fog.
Looking at the models, the MOS guidance is anticipating overcast
conditions at PANC for the next 24 hrs with the fog ebbing and
flowing around the airport.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Though there is an upper low currently parked over Southcentral
Alaska, shallow inversions and low level moisture have given rise
to areas of fog from Cook Inlet/Western Kenai, Anchorage Bowl, to
over the Matanuska Valley (especially Knik Arm). Stratus and fog
are more widespread across the Copper River Basin. Except for the
Copper River Basin, where the low conditions are expected to
linger into Saturday, the other aforementioned areas should see a
lessening of these conditions tonight with a little more mixing.
That said, there may be some patchy fog which redevelops/holds
overnight through the Knik Valley.

Pressure and temperature gradients will increase across
Southcentral tonight as cold air butts up against the interior
side of Alaska Range and Copper River Basin and flows through
gaps. Other than along the range, a noticeable increase in
outflow winds will be evident across the northern and Western
Gulf, including the eastern Kenai peninsula overnight which should
continue through Saturday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
With high pressure settling in over the Bering, dry, northerly
winds will dominate southwest Alaska through the weekend. This
setup will pull down Arctic air over the area dropping
temperatures to around -30 F for interior locations Saturday and
Sunday night. Winds look to be relatively light over the weekend
for low lying areas, but if they do pickup wind chills could
become a concern. However, there remains uncertainty with how
strong the winds will get.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
High pressure will dominate the Bering through the weekend with
the eastern side pulling down cold air over the eastern Bering and
Aleutians. These winds look to be around small craft strength
which will be enough combined with the cold air to bring freezing
spray to much of the eastern Bering. Out west, a North Pacific
system will approach the western Aleutians tonight but will be
stalled by the Bering high. This will keep its front and any
precip associated with it over the central and western Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term begins Sunday night and Monday with a high
amplitude upper high over the Bering Sea and a trough to the east,
which includes a closed low in the Gulf of Alaska and another over
northern Alaska. There is weak ridging in between the two lows
over Southcentral. Strong northerly flow will be over the Alaska
west coast and Alaska Peninsula. During the first half of next
week the Gulf low will slide east, and the Bering high will
weaken. This will allow the north Alaska low to dive southward,
reaching southern Alaska around the middle of next week. The exact
path and timing of this southward traversing low is not agreed
upon exactly by the models, but agreement is good enough for a
fairly high confidence forecast for this time range. The end
result of all of this is a fairly cold regime with temperatures
below normal over mainland southern Alaska. Some precipitation is
possible through the period for the Gulf coastal areas. There is a
chance some precipitation could get further inland, depending on
how the Gulf low behaves, but confidence in this is low.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 411 150 177 178 180 130.
         Heavy Freezing Spray  160 180 181 185.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...BL


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