Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 171315
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
415 AM AKST Fri Jan 17 2020

.ANALYSIS AND UPPER LEVELS...

A large upper level low centered over the Brooks Range combined
with a 514 Dm low in the Gulf is leading to generally benign
conditions across much of mainland Alaska. The subsequent zonal
flow and weakening pressure gradient is causing outflow gap winds
to continue to diminish across terrain gaps in the Chugach.
Precipitation will remain offshore, however as such the prevailing
easterly flow will bring onshore snow squalls to Kodiak and a
Winter Storm Watch is currently in effect with 6 to 12 inches of
snow possible Saturday morning.

A ~980 mb North Pacific low is bringing rain and/or snow to the
western and central Aleutians. Its associated inverted trough is
likewise bringing scattered precipitation to the Bering.

&&

.MODEL DISCUSSION...

Models remain in good agreement synoptically regarding the
aforementioned upper level pattern. As usual in this setup, the
main source of difficulty in this forecast lies with the snow
squalls over Kodiak associated with the moist, easterly flow over
the Gulf. Large scale models do not have the resolution to depict
mesoscale snow bands, while the mesoscale models do not agree on
where they will exactly occur over the Island.

&&

.AVIATION...

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

&&

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

A large upper high over the state will shift east through
Saturday night. Upper level flow over the area is from the east,
and will gradually become more southerly. A series of inverted
troughs is embedded in the easterly flow across the Gulf. These
features will help to enhance shower activity across the Gulf and
over Kodiak Island through tonight. Later today, a surface low
will develop over the central Gulf and quickly intensify as it
tracks toward Kodiak Island. As it does, widespread snow and gusty
northerly winds will develop over the island. The snow is
expected to become heavy at times for locations like Kodiak City
through Saturday morning. The combination of snow and winds
gusting to possibly as high as 40 mph will result in blowing snow
and reduced visibilities. The easterly flow will also act to bring
warmer air to the island by late Saturday morning. There is still
quite a bit of uncertainty for the details of this storm.

Inland portions of Southcentral will remain mainly clear and cold
through Saturday. Along the coast, some snow is possible at times
as systems pass westward through the Gulf.

&&

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

Cold temperatures and clear skies will persist across Southwest
Alaska today with high pressure still situated over the region.
Easterly waves moving over Kodiak and the Gulf bringing cloud
cover to the Bristol Bay region and the Kuskokwim Delta on
Saturday will be the key in how long the cold and dry conditions
last. Moisture will begin to move in near King Salmon and
Dillingham on Saturday afternoon, which could bring a few snow
showers to the surrounding areas. However, there is still
uncertainty in where these waves will track and the potential for
snow over the southern mainland.

Temperatures will see a slight rise over the next few days, which
will be dependent on when the cloud cover moves in. Clouds will
move over the Lower Kuskokwim Valley Saturday afternoon,
resulting in mostly cloudy conditions across all of Southwest.
This will keep the Lower Kuskokwim Valley the coldest spot once
again. By Sunday, the threat for snow showers over interior
Bristol Bay will diminish, but there could still be a few
lingering showers around the region.

&&

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

A front over the eastern Bering and Aleutian Chain will persist,
keeping gusty conditions in the forecast through the afternoon
when it begins to weaken. A gale force low sitting just south of
Adak this morning will keep on its track into the North Pacific
this afternoon. Snow showers stretching from Dutch Harbor to the
Alaska Peninsula associated with the active weather pattern will
allow for little snow accumulation through Saturday.

By Saturday afternoon, a new low will form just south of the
eastern Aleutians. However, there is still disagreement on the
placement of the low center and where the strongest core of winds
will be as it tracks northward through Sunday. Strong northeasterly
flow, along with widespread rain and snow showers, will continue
across the central and western Bering and Aleutian Chain through
Sunday.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

Marine weather still looks quiet in both the Bering and Gulf of
Alaska. A weak low pressure system will be present in the Gulf on
Monday, providing some localized areas of small craft advisory
winds on the north gulf coast. Then it moves inland and the Gulf
becomes quiet. The Bering will have light westerly flow, switching
to a light northeast late Tuesday. While low pressure is in the
area, we are confident it will be weak with little impact, so
moderate to high confidence in the marine forecast.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

The long term forecast starts off with the upcoming pattern shift
already taken place. A long wave, upper level trough looks to
exist stretching southeast across the Bering from Eastern Siberia
all the way down into the Gulf of Alaska. This means generally
unsettled weather for our forecast area to start the week. More
specifically, we are still expecting low pressure in the Gulf of
Alaska and zonal flow in the Bering and Southwest AK.

However, by Wednesday model agreement falls apart. Two of our
heavy hitters - the GFS and ECMWF - have very different solutions
for our forecast area, the Gulf of Alaska in particular. This
means past early next week there is not a good answer for the
forecast and we have low confidence in any solution past Tuesday.
We will have to wait and see what future solutions come up with.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 171.
MARINE...Gale Warning: 120 130-132 138 139 155.
         Heavy Freezing Spray Warning: 139 160 180 185.
FIRE WEATHER...NONE.

&&

$$

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



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