Area Forecast Discussion
Issued by NWS Anchorage, AK

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059
FXAK68 PAFC 100200
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKST Fri Nov 9 2018

.ANALYSIS AND UPPER LEVELS...
A broad upper level trough extends over the entirety of the
Bering. An upper level low anchoring this trough is centered
southwest of St. Lawrence Island. This low continues to bring
gale-force winds across the central and eastern Bering Sea today,
while the leading edge of the front associated with this low has
occluded and moved inland across Southwest Alaska. Behind the
front, showery precipitation is spreading in over the Pribilofs,
Southwest Alaska, and the northern AKPEN.

Looking south, an upper level ridge over the Gulf is gradually
moving eastward, allowing for an approaching North Pacific low
to become the main driver of the weather for this weekend.

&&

.MODEL DISCUSSION...
Models remain in generally good agreement for the near-term. All
model solutions agree that the upper level Bering low will move
southward and phase with a North Pacific low over the southwestern
Gulf of Alaska Sunday morning. Models then struggle with the
movement of this phased upper-level low over the Gulf through
early next week. Currently, the GFS solution was preferred, though
higher resolution models were used to resolve localized wind
forecasts and QPF amounts in the short term.

&&

.AVIATION...
PANC...Some MVFR conditions are expected early this evening,
becoming VFR later in the evening. VFR conditions are then most
likely through Saturday afternoon, but there is a chance of fog
late tonight through Saturday morning. Thus some VCFG was added
to the TAF.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A fairly robust Bering trough will dive southeast across the
eastern Aleutians/AKPEN overnight and phase with a low ejecting
north from Hawaii. The Bering trough was already very convective
looking with even some lightning strikes/flashes today, and then
add in the tropical moisture surging north and the pump is primed
for an energetic system to develop. Speaking of that tropical
connection, this afternoon`s layer precipitable water imagery
shows this surge is already taking shape, with the latest IVT
(Integrated Vapor Transport) showing forecasts of 300 to 400%
above normal.

An occluded front will move into the Gulf and approach coastal
locations during the day Saturday. Winds look to increase to Storm
Force over much of the northern Gulf, with Hurricane Force gusts
possible. This front will also bring precipitation to the region,
surging northward through the day.

Then, we`ll experience a brief "lull" in the activity, as we`ll
be in between systems with the AR shifting eastward and some
disturbances in the flow aloft passing overhead. as this occurs,
the surface front remains stalled along or just south of the
Southcentral coast allowing low-level colder air to remain in
place, while temperatures warm above freezing aloft (say above
4000 feet). This could bring some freezing rain to interior
locations Sunday morning.

On Sunday a new low will form and deepen south of the AKPEN. This
will influence the wind field as the pressure gradient tightens.
Significant rainfall is possible on the eastern Kenai Peninsula
Sunday evening into Monday morning, where some locations could
see 2 to 5 inches of rainfall in a 12 hour period.

&&

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

The long term forecast period commences with an active pattern
Monday featuring a large low centered in the Eastern Aleutians
with multiple embedded shortwaves. The most prominent being an
impulse along a surface gradient in the western Gulf of Alaska.
There are several things that stand out with this pattern. One...a
deep fetch of moisture will get steered into southcentral.
Two...this is a warm wet airmass with tropical origins, so expect
snow in the mountains and either rain or some type of mix in the
lower elevations. Three...the pressure gradient its tight, so
expect winds. The heftiest amounts of QPF are anticipated for the
Prince William Sound area for this event but the dynamics are such
that the Anchorage Bowl can also expect precipitation with
confidence. The longwave trough that is supporting this stormy
pattern lingers throughout the longterm period, resulting in broad
cyclonic flow for much of the Bering too.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast period commences with an active pattern
Monday featuring a large low centered in the Eastern Aleutians
with multiple embedded shortwaves. The most prominent being an
impulse along a surface gradient in the western Gulf of Alaska.
There are several things that stand out with this pattern. One...a
deep fetch of moisture will get steered into Southcentral.
Two...this is a warm wet airmass with tropical origins, so expect
snow in the mountains and either rain or some type of mix in the
lower elevations. Three...the pressure gradient its tight, so
expect winds. The heftiest amounts of QPF are anticipated for the
Prince William Sound area for this event but the dynamics are such
that the Anchorage Bowl can also expect precipitation with some
confidence. The longwave trough that is supporting this stormy
pattern lingers throughout the longterm period, resulting in broad
cyclonic flow for much of the Bering too.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 131 (Thompson Pass).
 Winter Weather Advisory 141 (South of Copper Center).
MARINE...Storm Warning 119 130 131 138 139 150 160 165 175>177
                         180.
 Gale Warning 120 132 136 137 140 155 178 179 181 185.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...PJS



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