Area Forecast Discussion
Issued by NWS Anchorage, AK

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619
FXAK68 PAFC 161303
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
403 AM AKST Thu Jan 16 2020

.ANALYSIS AND UPPER LEVELS...

The overall large scale pattern remains generally unchanged from
yesterday. A sharp, negatively tilted upper level trough extends
from the Kamchatka Peninsula through the central Aleutians. Its
associated front is bringing gusty southeasterly winds and locally
heavy rain to this region. The upstream ridge has subsequently
shifted slightly eastward and transitioned into a large, closed
upper level high centered over the Seward Peninsula. This is again
inhibiting the development of any precipitation or much cloud
cover over much of the western portion of the state, although
these conditions may lead to fog in low-lying areas. Strong
outflow winds have diminished in the Chugach terrain gaps as the
aforementioned high has caused a more zonal flow pattern over the
Copper River Basin. This is also preventing the northward
progression of a low near the Panhandle and thus all precipitation
is likely to remain offshore for the near future.

&&

.MODEL DISCUSSION...

Synoptically, models remain in good agreement. There is still
slight uncertainty with regards to how a small low will interact
with the aforementioned main frontal system west of the Pribilofs.
However this will likely be only of minimal impact as the front
will already be weakening, thus diminishing the southerly gales in
the eastern Bering.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

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

A broad upper ridge over the mainland with cold interior air at
the surface will continue to support strong offshore flow and
gaps winds across Southcentral through today. Areas of blowing
snow are expected across the Matanuska Valley through today. Offshore
flow and gap winds will slowly diminish tonight and through
Friday as pressure gradients relax and winds aloft weaken. Broad
easterly flow with waves moving west across the Gulf will bring
snow showers to Kodiak through today with a couple inches of fresh
snow expected. Snow showers will diminish some tonight, but will
become more numerous Friday and Friday night with the next wave.
This next batch on Friday night will also be accompanied by gusty
northerly winds, so there may be some blowing snow issues.

&&

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

High pressure situated over interior Southwest Alaska will help
to keep cold air stretched across the region with clear skies and
dry conditions. Temperatures tonight and Friday afternoon will see
a slight downward trend before warming up a bit for this weekend
as cloud cover starts to move in across interior Bristol Bay.
However, clear skies through Saturday over the Lower Kuskokwim
Valley will keep this area the coldest in Southwest Alaska with
low temperatures near 20 below zero.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

The gale force front stretching from the north central Bering to
the central Aleutians and Alaska Peninsula this morning will
persist through this afternoon. The Pribilofs are the dividing
line of the front with southeasterly winds from the Islands into
the eastern Bering, while areas west of the Pribilofs will see
more of a west to northwesterly flow of winds through the morning
hours today. Areas north of the Chain can expect to see strong
winds and gusts out of bays and passes before the front begins to
weaken to small craft level winds through the night. Widespread
rain and snow showers will continue across much of the Bering
associated with this frontal system.

To the west, a front associated with a gale force low will cross
over the western and central Aleutians by this afternoon, which
will make a quick exit back into the North Pacific overnight and
into Friday morning. This warm system should keep any new
precipitation as rain or a rain snow mix as it moves over the
region.

&&

.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 with 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: 119 121 127 130 139 160 180
                                       185.
         Gale Warning: 127 130 138 155 165 170-174 176 177 180
                       181 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...BB



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