Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 201301
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT Fri Sep 20 2019

.ANALYSIS AND UPPER LEVELS...

A long wave trough currently resides over southwest AK and is
extending southeast from an upper level low located in the
Chukchi Sea. This trough is pushing northeast and is supporting
the low pressure system that is currently moving into Southcentral
AK from the Gulf of Alaska. Behind this trough, zonal flow
continues right over the Aleutian Chain, furthering the rapid
succession of low pressure systems through our forecast area.
Indeed, the next two lows are already lined up. One is a weak low
currently moving through the Bering Sea and will impact Southwest
AK tomorrow. The other is a more significant low that is just
entering the western Aleutians and will make its way east,
entering the Gulf of Alaska Sunday into Monday.

&&

.MODEL DISCUSSION...

Models continue to perform well in the short term. Differences do
emerge with respect to a low pressure system moving into the Gulf
Monday, so there is some uncertainty there. However, they agree
enough for us to know the next system of importance will be moving
into the area Sunday into Monday. So, we still have confidence in
the forecast, even if particulars need to be ironed out.

&&

.AVIATION...

PANC...A low pressure system moving through the area will provide
the possibility for MFVR ceilings this morning. Otherwise, expect
overcast skies with light rain, but conditions remaining VFR.
Winds will be light out of the north.

&&

.FIRE WEATHER...

Another low pressure system moving through Southcentral AK is
bringing steady rain to areas around fires. Enough precipitation
should fall to produce wetting rains. Weather will continue to
remain cool and damp after the exit of the low.

&&

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

The biggest forecast question for today involves the track of the
low in the Gulf and how far east it will go in the Prince William
Sound area. It looks as though the low will enter the eastern part
of the sound instead of the western part today. While this is a
small difference, it will make a difference in how soon the rain
on the western edge of this system ends or at least becomes much
lighter. The Anchorage Bowl and Matanuska Valley will be near
this edge today and tonight and that is why this may be noticeable.
Therefore, lowered the amount of QPF expected over Anchorage and
the Mat-Su valleys, but kept the POPs rather high. This is because
there will still be some light rain, but the heaviest amounts
look to be farther to the east over the Chugach Mountains.

After this system clears to the east there will a short break
before the next system moves into the area from the southwest late
Sunday. This break may bring in widespread clear skies Saturday
night which would likely bring in the first freeze of the season
to areas such as east Anchorage, the Butte, and near Kenai.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Fri-Sun)...

Cool temperatures, northerly flow, and patchy fog remain across
Southwest Alaska for this morning. Showers across Bristol Bay and
the Kuskokwim Valley will diminish through this afternoon as the
current system moves eastward out of the region. Low temperatures
overnight will once again dip near the freezing mark across the
region as clearing conditions continue before the next front
approaches the southwest coast for Saturday. Widespread precipitation
will move inland over the Kuskokwim Delta and Bristol Bay by
Saturday afternoon as the front lifts northeastward through Sunday
morning.

A new and stronger low moving inland from the Bering will become
the dominant feature by Sunday afternoon, keeping a track farther
south than the previous feature. This will bring another another
shot of widespread rainfall to the the Alaska Peninsula and
Bristol Bay region.

&&

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

The eastern Bering and Bristol Bay will continue to see northwesterly
small craft advisory winds associated with the low that has moved
into the gulf. Strong gap flow along southern portions of the AKPEN
will continue to see the potential for gale force winds out of bays
and passes, which will slowly diminish through Saturday morning.

A second feature of interest is the low in the northern Bering
this morning that will keep small craft winds and it moves towards
the Pribilofs for Saturday morning. Winds will weaken as the low
moves inland over the Y-K Delta coast by Saturday afternoon.

By Saturday afternoon, a strong low approaches the central
Aleutians moving in from the North Pacific. Small craft winds,
increasing to gales, will accompany this low feature, stretching
out into the central and eastern Bering Saturday through Sunday.
The possibility of storm force winds on the back side of this low
cannot be ruled out as winds move over the central Aleutians, from
Dutch Harbor to Cold Bay.  Models are still uncertain about the
exact position of the low center, but this low is expected to
strengthen as it moves eastward for Sunday.

&&

.MARINE (Days 3 through 5)...

Starting Sunday, winds in the Gulf will diminish as a low exits to
the east. Small craft advisory level seas driven by fresh swell
will persist Sunday morning, but likely diminish by the afternoon.
Attention turns to a low currently developing south of the
central Aleutians. Gales are expected over the central and eastern
Aleutians by Sunday, then models continue to project a triple
point low developing late Sunday into Monday that would bring
gales into the Gulf. There`s uncertainty with the path/strength
of the secondary low, but at this point confidence is growing that
there will be gales in the Gulf Monday, possibly persisting into
Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

A relatively progressive pattern will continue as a low traverses
the Aleutians, bringing widespread precipitation and gusty winds
to the Aleutians Sunday. The Southwest mainland will probably see
some precipitation from this system, especially over the AKPEN...
but the primary impacts will be felt over the Aleutians. The low
is expected to track into the Gulf. Thus, as the low progresses
eastward Sunday into Monday, precipitation is expected over Kodiak
Island and the North Gulf Coast. Farther north, east/northeast
flow will prevail and relatively dry weather is expected. An
Arctic trough over the Bering Strait will strengthen by midweek,
maintaining relatively cold conditions and unsettled weather over
southern Alaska. Another low will develop in the central Bering
Thursday into Friday, but it`s too early for confidence in
details.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING: 120 125 130-132 138 351 352
         STORM WARNING: 119 150
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...DK


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