Area Forecast Discussion
Issued by NWS Anchorage, AK

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565
FXAK68 PAFC 140134
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKST Mon Jan 13 2020

.ANALYSIS AND UPPER LEVELS...
A weak upper level ridge is over the Alcan border this afternoon
with largely zonal flow over the Bering Sea. This zonal flow is
starting to be disrupted by an amplifying upper level ridge in
the western Bering Sea which will become a major feature by the
middle of the week. The 250 mb jet stream is already reflecting
this amplification in that a jet streak of around 100 kt has
developed over the northern part of this ridge in the northwest
Bering Sea with a speeds closer to 80 kt at 250 mb over the
eastern Bering. This jet streak will increase over the next few
days with this ridge.

&&

.MODEL DISCUSSION...
Models remain in good agreement in the synoptic and all have the
large upper level ridge amplifying in the Bering Sea during the
middle of the week. As is typically the case with good model
agreement, higher resolution models were used to try and refine
winds as temperature forecasts will be highly dependent on the
wind speeds and when there will be enough wind to mix-out the
inversion.

&&

.AVIATION...
PANC..Some stratus has lingered around the airport this afternoon
in the wake of last night`s snowfall. It does look like drier air
will move into the area and improve the ceilings this evening.
After the stratus lifts it should be VFR conditions for awhile.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Clouds are scattering out over Southcentral as a ridge builds
over the Bering Sea and surface low pressure in the Gulf of Alaska
exits to the southeast. Tonight, temperatures will return to (or
stay in) the negatives for most of Southcentral. Exceptions
include Kodiak Island, Prince William Sound and coastal areas on
the Kenai Peninsula. Continued clearing and stable conditions will
also set the stage for fog over inland areas Tuesday morning. A
cooling trend will continue at least through Wednesday as Arctic
high pressure at the surface strengthens over the Alcan. Offshore
winds out of the usual gaps and passes (Valdez waters,
Resurrection Bay, Whittier and the Copper River Delta) will ramp
up tonight and Tuesday, remaining elevated at least through
Wednesday. A Wind Chill Advisory remains in effect for Thompson
Pass through Wednesday morning. Depending on the amount of
cooling, Broad Pass and the Matanuska Valley will need to be
monitored for potential wind chills down to 40 below late Tuesday
into Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
An area of high pressure will continue building into the area
through Tuesday, eventually moving overhead. This will gradually
reduce the onshore flow and turn the winds briefly calm and then
offshore by Wednesday. This will keep snow shower activity and low
stratus and fog in the area both tonight and Tuesday night, ending
by Wednesday. That same high pressure will strengthen over the
interior into Thursday. That will very effectively block the
highly active western Bering storm track from moving into the
area. Thus, expect clearing skies by Thursday with a cooling trend
in the temperatures.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
High pressure over the central Bering will move into the eastern
Bering by Tuesday morning, then gradually move into Southwest
Alaska Tuesday night. Underneath the high, conditions will be
relatively quiet, with some snow shower activity, some stratus,
but nothing much to talk about. All of the real action will be
over the western and eventually central Bering. A strong low will
move near Shemya Tuesday morning dragging a front behind it. Ahead
of these features, southeasterly winds will strengthen as the
winds squeeze in between the low over the western Bering and the
high over the eastern Bering. This strong pressure gradient will
kick the winds up to 60 kt over the open waters of the western
Bering. It will also bring in much warmer air as well. The low
will track due north into Kamchatka, as its attending front moves
into the central Bering on Wednesday. Another low will form along
the front on Wednesday, though where exactly it forms is a big
question, with significant disagreement between the models. On the
eastern (warm) side of the low, the winds will kick up once again
into storm force, this time just west of Unalaska Island and up
to the Pribilofs. Once this low moves to the north, the front as a
whole will fall apart by Thursday over the eastern Bering, with
gale force winds expected from Dutch Harbor through the Alaska
Peninsula. Another separate low moves into the western and central
Aleutians on Thursday, but the strengthening high pressure over
mainland Alaska looks to shunt that low to the south and east back
into the North Pacific.

&&

.MARINE (Days 3 through 5)...
Thursday through Friday the main focus for gales winds are
expected over the Bering as a front slowly lifts north. There is
potential that winds could be stronger Thursday morning across the
Aleutians, however model uncertainty remains high. The next low to
monitor for the Gulf develops across the eastern waters on
Saturday night and then tracks northwest into Sunday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Dry and cold conditions are currently forecast across the southern
mainland Thursday night through the beginning of next week with
active weather mostly impacting Bering. There is a bit of
uncertainty between the models, so the forecast was trended toward
a blend of ensembles which increases precipitation across the
eastern Bering and Gulf during the upcoming weekend.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 131.
 Flood Advisory 121.
MARINE...Storm Warning 173>175 177 178 185.
 Gale Warning 127 130 131 132 138 150 170>172 176 179.
 Heavy Freezing Spray 119 121 126 127 129 139 160 180.
FIRE WEATHER...NONE.

&&

$$

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



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