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449
FXAK68 PAFC 160245
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
545 PM AKST Wed Jan 15 2020

.ANALYSIS AND UPPER LEVELS...
The highly amplified upper level ridge remains along an axis that
runs from the Alaska Peninsula through the Bering Strait. A jet
streak is oriented from north-to-south over Southcentral Alaska at
over 100 kt at the 250 mb level which is helping to increase winds
over the region. The surface front over the Bering Sea and into
the North Pacific had a low develop along it which resides
between Adak and Atka today. This front and low is the source of
the strong winds in the Aleutians and Pribilof Islands as it is
squeezed against the strong surface high over mainland Alaska.

&&

.MODEL DISCUSSION...
The only short term model issue revolves around the low that
developed along the front in the Bering Sea. This front is
elongating as it pushes into the ridge over mainland Alaska which
is shearing the front apart. This is causing the models to have
some very different solutions as to whether the low is able to
remain with one center as it weakens or break into numerous weak
low centers. The biggest result of all this is to bring increased
uncertainty to the Eastern Aleutians and Pribilof Islands regions.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds will persist. The
northerly winds have dissipated all the fog around Cook Inlet and
through the Mat-Su Valleys so redevelopment looks highly unlikely
overnight or tomorrow morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3;
Tonight through Saturday)...
In the upper levels, there is a northerly jet streak situated
over the state along with a vigorous shortwave diving south across
Southcentral. These features, combined with arctic air returning
to the interior as well as a strong surface pressure gradient
between a building ridge in the interior and a trough in the Gulf,
are acting to enhance the gusty outflow winds across not only for
coastal locations, but through interior gaps and passes. This
includes locations such as Thompson Pass and the Matanuska Valley
where winds gusts of 40 to 60 mph are occurring and are expected
to continue through Thursday. For other wind-prone areas, gusts
will not be quite as strong, but will persist through the next 24
to 36 hours with gales continuing across the Valdez waterways.

Elsewhere, clouds and a few snow showers are skirting the eastern
Prince William Sound coast this afternoon. However, the bulk of
the moisture will remain south of the land areas, as the compact
polar low responsible for the precipitation continues to track
south and west. This area of low pressure will move toward
Kodiak Island tonight, with snow showers developing this evening
and lingering through the overnight hours. For Kodiak City, an
inch or two of snow is possible by tomorrow morning.

By Friday, the winds will die down as the flow aloft turns more
easterly in advance of a shortwave lifting north from the southern
Gulf. This feature will also act to increase clouds and
precipitation across the Gulf and Kodiak Island, and possibly
as far north as coastal Prince William Sound and Kenai Peninsula.
By Saturday, this system slides west to the AKPEN as the next
surface low lifts north toward the northern Gulf.

&&

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

Cold and quiet weather persists across Southwest Alaska through
Saturday. High pressure over the interior will keep the cold air
flow moving offshore. The air mass is being slow to cool, due in
part to a not quite as cold air mass over the interior and a lot
of high clouds around so temperatures for tonight and tomorrow
have been raised some. Lows to 20 below zero are still expected
over the Lower Kuskokwim Valley both Friday and Saturday nights.

&&

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

The very active weather pattern that has been present over the
Bering Sea will shift to a much less active one over the next
3 days. The strong front draped from south to north across the
central Bering, essentially splitting the basin in two, remains
the focus of the most active weather. There have been a number of
gusts in Nikolski exceeding hurricane force over the day today.
The worst of the storm is occurring right now, so through this
evening the winds should begin dying down all along the central
and eastern Aleutians. The winds will persist longer further north
across the Pribilofs, lasting until the front moves over the
islands early Thursday morning. By that point, the entire front
will be rapidly weakening, and also retrograding back to the west.
Thus, there may be a time in the Pribilofs where the winds switch
around to the west or southwest, but by Friday evening, winds will
return back to the southeast when the front moves back to the
west. The retrograding front will be the result of strengthening
high pressure over interior Alaska, whose northeasterly winds will
push the front back the other way. It will continue weakening the
entire time, effectively dissipating on Friday night.

A separate low will approach the western and central Aleutians
starting Thursday morning. Unlike the last low, this one will
follow a very different track; moving east along the chain on
Thursday and then gradually drifting south back into the North
Pacific. Impacts from this low in these areas will be much less,
likely including rain or a rain/snow mix with gusty easterly
winds. For now it appears just a bit too warm and the winds a bit
too weak in these areas to be concerned about a blizzard. By
Saturday, the flow over most of the Bering will be weak, but with
occasional spin-ups of very small lows expected in various areas
across the Bering, namely in the area where the westerly winds
over the western Bering meet with the easterly winds from mainland
Alaska.

&&

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

Marine weather looks quiet in both the Gulf of Alaska and the
Bering Sea. A pattern shift over the weekend will quiet weather in
both areas. As of now, winds in the Bering will shift to a light
westerly flow Saturday into Sunday. In the gulf, winds will
maintain a general easterly direction until Monday but with
offshore gusts ceasing Saturday. Monday in the gulf a weak low
pressure system moves in, but right now it does not look to
elevate winds and waves very much. Confidence is high in this
forecast as models are locking on the pattern shift.

&&

.LONG TERM FORECAST (Days 4 through 7:Sunday through Tuesday)...

Over the weekend we are expecting a pattern shift for our
forecast area. The dominant omega block currently in place is
expected to break down, with the high pressure closing off and
retreating to the north and east. It will also lose some strength
as well. The breakdown of this blocking pattern will allow a weak
low pressure system to move into the Gulf of Alaska, increasing
the chances of precipitation along the coast starting Monday. It
will also shift wind direction and allow a warm-up in temperatures
to more seasonable conditions for Southcentral Alaska. Out west,
this pattern shift will allow for more zonal flow across the
Bering and into Southwest Alaska. At this time, no significant
weather features are embedded in this pattern out west.

We are confident this shift in the pattern will occur. We are also
confident the warm-up for Southcentral will not be too strong, so
we will stay below freezing and keep our snowpack. What is lacking
in confidence is the setup of the low in the Gulf of Alaska, as
models disagree on its position. So we`ll have to hone the details
in the short term on how much snow falls and where. So, high
confidence in a new pattern, low confidence in the particulars.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 119 127 129 139 140 141 160
                                      180 185.
 Storm Warning 170.
         Gale Warning 127 130 155 165 171 172 173 174 175 176
                      177 179 180 181 185.
FIRE WEATHER...NONE.

&&

$$

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