Heavy Freezing Spray Warning 92, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
609 PM AKST Fri Dec 9 2016

.ANALYSIS AND UPPER LEVELS...
Upper level ridging persists over the Arctic Ocean while a broad
trough extends from a low centered offshore of the Pacific
Northwest to the Alaska Peninsula then turns and extends across
the Kuskokwim Delta and into interior Alaska. An upper level low
within this broader trough crossed the Alaska Peninsula this
morning and continues southeast towards the southwestern Gulf.
Snow showers and breezy north winds associated with this upper
low are currently impacting the Alaska Peninsula but should taper
off this evening as this feature moves further away. While cold
north to northeasterly flow persists across Southwest Alaska, mid-
level easterly flow continues to bring snow showers across the
Aleutian Range and into the greater Bristol Bay area. Further to
the west a frontal system is pushing into the western Aleutians
with an upper level ridge amplifying over the central Aleutians
and Bering.

Over Southcentral Alaska offshore flow continues. A trough
extending from a surface low south of Kodiak Island up to the
southern Kenai Peninsula continues to rotate west with
precipitation tapering off from north to south behind it. Further
north, clear skies prevail with breezy north winds through the
Susitna Valley and south down Cook Inlet Brushing west Anchorage.
The offshore pressure gradient across the northern Gulf Coast
remains strong with sustained northeast winds averaging 45 to 50
mph through Thompson Pass. The center of the surface high is
currently dropping south through the Yukon Territory following an
associated arctic trough.

&&

.MODEL DISCUSSION...
Models are in good synoptic agreement both on the offshore flow
and the front approaching the Aleutians. Higher resolution models
were preferred for capturing wind details.

&&

.AVIATION...
PANC...VFR conditions will persist with fairly light north winds.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The weak wave pushing through the western Gulf will bring light
rain and snow to Kodiak through the night and then diminish
tomorrow. Another wave is tracking south through Southcentral
Alaska and as it pushes into the Gulf tonight it will help to
enhance outflow winds, especially in the north to south oriented
gaps. Outflow winds will then continue, but diminish, into Sunday.
In this setup Southcentral will see few clouds and little to no
precipitation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Despite a few snow showers this evening across Bristol Bay, clear,
dry and cold conditions will persist through much of the weekend
as ridge settles across the interior to the Southwest. Offshore
flow diminishes Saturday night which will allow for patchy fog
development across valleys early Sunday, but conditions are
expected to improve shortly after sunrise. A front approaches the
Kuskokwim Delta Sunday afternoon. Southeasterly flow develops in
the afternoon with increasing chances for snow Sunday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A front stalls along the western and central Aleutians tonight
then makes slow north and eastward progress on Saturday. Gale winds
accompany the front along with rain. Snow showers will also
develop ahead of the front as the warm moist air mass glides north
over the colder polar air currently in place. The boundary is re-
enforced on Sunday as another surface low develops in the North
Pacific. This surface low puts the front into motion with the
boundary expected to move into the Central and Northern Bering by
Sunday afternoon.

&&

.LONG TERM FORECAST (Days 3 through 7...Fri through Tue)...
Sunday evening and beyond, a weakening front over the Eastern
Bering Sea will move into Southwest Alaska before falling apart as
the strong ridge over Southcentral shears it apart. Thereafter, a
series of strong storms look poised to move through the Bering Sea
beginning Monday night. By Wednesday, there is increased uncertainty
with how strong the ridge over mainland Alaska will be as these
Bering storms attempt to shift the ridging eastward. The ECMWF is
an outlier which holds a much stronger ridge in place over the
Southern Mainland, keeping most of Southern Alaska dry until late
in the week. The Canadian GDPS and GFS are more bullish in sending
energetic waves over the top of the ridge by Wednesday night and
shifting the ridge eastward. For now, an ensemble approach
favoring a easterly shifting ridge axis was preferred which will
begin to highlight precipitation chances by mid to late next week
and into next weekend. This pattern will dramatically shift the
sensible weather as clouds and moisture will likely result in
warming temperatures...along with the threat for snow turning to
rain/snow by the weekend as the Northeast Pacific ridge expands.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 127 128 175 176 177 178.
Heavy Frz Spray 126 127 160 180 181.

&&

SYNOPSIS AND MODEL DISCUSSION...JR
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...JA/TP