Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 270116
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
416 PM AKST Sun Feb 26 2017

.ANALYSIS AND UPPER LEVELS...
A large upper ridge over the north Pacific extends north to over
mainland Alaska. The flow across the mainland has become nearly
zonal (westerly) as the northern periphery of the ridge is being
flattened by an eastward moving upper wave. Moisture rounding the
top of the ridge, associated with a broad surface front, brought
snow across portions of Southwest Alaska. Due to downsloping
conditions east of the Alaska/Aleutian Range, most areas across
Southcentral were dry except for upslope areas along the Talkeetna
Mountains and portions of the Copper River Basin. Mid and high
clouds are starting to clear across Southcentral revealing low
stratus from the Mat-SU Valleys south to Cook Inlet and the
western Kenai Pen. The strengthening low pressure trough over the
northern Gulf produced brisk westerly winds across the western
Gulf/western Prince William Sound.

&&

.MODEL DISCUSSION (through Tuesday afternoon)...
The numerical models through Tuesday afternoon are in fairly good
agreement. The NAM/GFS will be generally used in the West. The NAM
generally looks good for use in the east. Hand edits will also be
needed in the east to address strong gap flows Monday night.

&&

.AVIATION...
PANC...IFR to MVFR Cigs may break up some this afternoon but will
more likely reform again tonight. With the presence of this cloud
deck expect visibilities to remain higher than the past couple
days, though there still may be some reduction at times.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The abundant valley stratus has persisted through much of the day
and is only now partially breaking up this afternoon. With low
level winds relatively light tonight and flat ridging persisting,
expecting to see the stratus to fill back in again overnight
although fog should remain sparse and patchy. A cold upper level
trough will swing into Southcentral Alaska from the northwest
Monday afternoon bringing a brief period of light snow during the
afternoon and evening. Expecting to see snow totals around a half
of an inch for most locations with up to two possible along west
facing slopes where cold advection snow showers will last longer.

Northwesterly gap winds will increase sharply following the
passage of the upper level trough Monday afternoon and evening.
Expecting to see storm force winds through the Barrens and out of
gaps and passes in the Alaska/Aleutian range impacting portions of
Shelikof Strait and Cook Inlet. Additionally, westerly winds will
build through eastern Turnagain Arm, Portage Valley and Whittier,
with northerlies building through Broad Pass and Resurrection Bay.
North to northeasterly winds will then become very strong through
Thompson Pass as the northerly offshore pressure gradient builds
along the northern Gulf Coast through midweek with the chance for
these stronger winds to mix down into Valdez at times Tuesday and
Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Light snow and rain will continue to linger over the Southwest
mainland through this evening, and become more showery overnight
as the front shifts further southeastward over the Alaskan and
Aleutian Ranges. Accumulating snowfall is expected to remain
mainly along the mountains through Monday evening, with snow
shower activity over the remainder of the Southwest mainland
persisting through Tuesday morning. However, there could be a few
lingering pockets of rain or mixed precipitation confined to the
Bristol Bay coastal areas through this evening. Cooler air from
the north will begin to filter in behind the aforementioned front
tonight, starting a colder trend in temperatures that looks to
persist through much of this coming week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure building into the Bering will continue to push the
front southward through Monday. Rain and snow over the eastern
half of the Bering and Aleutians will diminish and switch to snow
showers on Monday before tapering off. A front associated with a
low just east of the Kamchatka Peninsula Monday will bring some
warmer and moist air from the North Pacific over the Western
Aleutians and Bering. This system will bring another round of
gale force gusts and rain through mid week from Atka west.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The developing upper level trough over the mainland will close a
center off over the Gulf by mid week while a dominant ridge
centers over the western Bering. Northerly flow between these
systems will keep a colder pattern over the southern mainland
through the end of the week. Strong shortwaves diving along the
west coast will re-enforce cold air along with gusty winds. A
drier pattern mid week may need to adjusted as moisture begins
to round the eastern side of ridge along with a stronger short
wave propagating in from the Arctic closer to Friday. Models
were in better agreement with the synoptic pattern today. The
ECMWF/ensembles were favored for run to run consistency in the
extended forecast.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray Warning 121 129 130 136 137 138 139
160 180 185. Storm Warning 130 131. Gale Warning 120 121 129 132
136 137 138 139 150 177 178.

&&

$$

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


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