Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 150122
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
422 PM AKST Fri Feb 14 2020

.ANALYSIS AND UPPER LEVELS...

A large area of low pressure over the central Bering is currently moving
northeastward. An occluded front associated with this low is
currently bringing areas of light snow and freezing drizzle across
the Kuskokwim Delta and over northern Bristol Bay. Upper-level
ridging is gradually shifting eastward across mainland Alaska. The
polar jet remains south of the Aleutians and then extends
northeastward into southeastern Alaska. A triple point low east
of Kodiak is moving northeastward in the Gulf of Alaska.

&&

.MODEL DISCUSSION...

Models remain in good agreement with the overall synoptic pattern through
Saturday. However, discrepancies begin on Sunday with a
developing low over the western Bering/Aleutians. After Sunday,
models show a series of lows moving northeastward across the
Bering/Aleutians and Gulf of Alaska with significant differences
in intensity and storm track. Due to the widespread variation
between guidance, the forecast confidence after Sunday remains
low. A couple areas of confidence after Sunday are that the
weather pattern will be active, and warmer temperatures are likely
Monday and Tuesday. High resolution models were preferred in the
short term for this forecast package to resolve local effects.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3...Tonight through Monday)...

A dissipating occluded front will continue to bring some very
light snow to the southern end of the Kenai Peninsula through
early this evening. Meanwhile, the upper level ridge that brought
cool and dry conditions along with offshore flow will move
over Southcentral tonight, helping to end any remaining gap winds
along Prince William Sound. The ridge will exit northward on
Tuesday as a broad trough with weak short-waves move in from the
Bering Seas. None of these waves looks strong enough to produce
much, if, any precipitation. Thus, weather looks to remain quiet
over Southcentral with continued mostly dry and cool conditions
through Sunday morning.

The zonal flow aloft that has been persistent with the pattern
the last couple days will rapidly amplify beginning Saturday night
near the western Aleutians. This amplification of the pattern
will send a warm front northward across Kodiak Island and the
western Gulf on Sunday. Precipitation will start as snow, but
transition to rain as warmer air moves northward. This warm front
will continue northward into Southcentral Sunday night into
Monday, bringing areas of light snow. Temperatures will begin to
rise, but will remain below freezing across all but perhaps the
southern tip of the Kenai Peninsula.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Increased chances for snow continues as a parent low over the
western Bering sends several upper level waves over the Southwest
as it lifts north this weekend. A front across the region from
near Aniak to Iliamna weakens through the evening, however
isolated to scattered showers will develops along this boundary
as short waves moves overhead. A secondary front pushes to the
southwest coast just before midnight tonight, then continues
slowly eastward through Saturday.

The next better organized front develops on Sunday morning along
the southern Bering lifting north across the Alaska Peninsula in
the afternoon. Precipitation will spread across Bristol Bay
Sunday evening, progressing northward across the Kuskokwim Valley
and Delta overnight.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A 970 mb low over the central Bering weakens as it lifts north
through Saturday. A short wave ridge provides a brief break in the
active pattern across much of the waters Saturday night. However,
the next North Pacific Storm brings gusty gale winds across the
western waters Saturday night with a surface low deepening to 970
mb Sunday morning. The parent low driving this system organizes as
cold air advects around the base of its trough. There is still a
bit of uncertainty on the development on this storm as models are
still working out the dynamic details. Added blowing across the
western Aleutian Chain Saturday night

&&

.MARINE (Days 3 through 5/Monday through Wednesday)...
Expect multiple deep lows over the eastern Bering Sea down into
the North Pacific on Monday. All of this will shift eastward, with
one or more strong lows tracking into the Gulf of Alaska Monday
night through Tuesday. Forecast confidence remains high in the
overall pattern, with support for gale to storm force lows.
Meanwhile, forecast confidence in the track and strength of each
individual storm is low.

Meanwhile, it is looking likely that another large and deep low
will move to the western Aleutians Tuesday, then quickly track
eastward across the Bering and Aleutians on Wednesday. Once again
expect widespread gales with potential for storm force winds.

&&

.LONG TERM FORECAST (Days 4 through 7/Tuesday through Friday)...
While model agreement is poor in the Monday/Tuesday time frame,
solutions converge upon the same general solution beginning with a
deep low tracking to the western Aleutians on Tuesday. A strong
zonal jet will drive this system quickly eastward, across the
Bering Sea and Aleutians and into the Gulf of Alaska on Thursday.
The GFS solution takes the track a bit farther north, but
ensembles support the more southern track. Based on this, expect
another round of strong winds and heavy precipitation as the storm
system crosses the area. The southern track would keep
precipitation primarily in the form of snow across the southern
mainland of Alaska Wednesday night through Friday.

On the back side of this storm, Arctic air will plunge back
southward across the entire forecast area. Thus, expect well below
normal temperatures to settle back in across Southwest Alaska late
next week, then into Southcentral Alaska by next weekend. Upper
level flow will remain progressive, so it looks like another deep
low will reach the western Aleutians by Friday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 173-177 185.
 Heavy Freezing Spray 185.
FIRE WEATHER...NONE.

&&
$$

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


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