Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 171353
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
453 AM AKST Sat Feb 17 2018

.ANALYSIS AND UPPER LEVELS...
A high amplitude long wave ridge is currently over the western
third of the mainland and moving east over southcentral bringing
rather tranquil weather to the southern half of the state.
Clearing skies and rather weak offshore winds have lead to the
development of low stratus and fog over the Knik Arm and Anchorage
Bowl early this morning. Further west, satellite imagery shows a
broad cirrus shield advecting north and east over the top of the
ridge out ahead of a longwave trough which is located over the
western Bering Sea. A strong southerly jet is currently moving
over the central and eastern Aleutians supporting a surface low in
the Bering. A front out ahead of the low is sweeping east across
the island chain bringing storm force winds and heavy rain to
places like Dutch Harbor and Akutan.

&&

.MODEL DISCUSSION...
Models remain in good agreement through the mid-term as a front
moves across SW Alaska Sunday morning then falls apart as it
reaches southcentral by Sunday night. All models have now come
into agreement that as the front reaches southcentral the main
lobe of energy will split off from the trough and form a weak
surface low in the Gulf, keeping most of the precipitation well
south of southcentral.

&&

.AVIATION...
PANC...Clear skies and weak flow have led to the re-development
of low stratus over the Knik Arm early this morning, which has
advected into the Anchorage Bowl, staying mostly over south and
west Anchorage so far. Webcams show the stratus to be patchy in
nature so only expect intermittent LIFR conditions over the
terminal this morning before clearing up by noon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level ridge will slowly move eastward across southern
Alaska through tonight. The low level flow is fairly weak inland,
and some fog is expected, especially near Cook Inlet. On Sunday
an upper level trough will move through the ridge. This will bring
rain to Kodiak Island beginning around noon and ending some time
in the evening. Precipitation chances are less further north, but
there is at least a slight chance Sunday evening for the Cook
inlet area through the Susitna Valley. This system will rapidly
move east, exiting into Canada Monday morning.

&&

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

A high amplitude upper level pattern is in the midst of developing
this morning as ridging aloft builds over Southwest Alaska. Dry
offshore flow will be dominant today and this evening before the
warm front over the Bering Sea moves inland tonight and moves
eastward through Sunday. Enough cold air will be in place for at
least some snow across most of Southwest Alaska although rain will
likely mix in, especially along the immediate coast line and in
the lee of the large mountain ranges. The heaviest snow
accumulations will be from Dillingham north and west where 2 to 5
inches of snowfall is possible. The front clears the Alaska Range
Sunday evening with dry conditions remaining through the daytime
Monday.

&&

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

The storm track will remain over the Bering Sea for the
foreseeable future as a strong gale force front this morning moves
east toward the Southwest Alaska coast. Gusts along the Eastern
Aleutians will reach into the low 60 MPH range, especially in
favored gaps with southerly winds.

A large gale force low (with some storm force winds mixed in)
over the Western Aleutians will move into the Bering Sunday and
will remain over the Bering Sea through Monday as it slowly tracks
northward toward the Bering Strait. Long fetch southwest winds
behind the low will support sea states as high as 30-35 feet on
Monday and Monday evening over the Bering Sea outer waters.

&&

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

Long term period starts off with increased uncertainty due to
models suddenly diverging with the movement of the low across
Southcentral Alaska and the Gulf of Alaska. Most reasonable
approach to Sunday night through Monday is to nudge precipitation
chances down over most of Southcentral Alaska and increase them
some in the Gulf. The Bering Sea storm at that same time frame
seems to still be on track with a deep low in the western Bering
Sea and general south to southwest flow over most of the Bering
Sea into Southwest mainland Alaska. After Monday, there is still a
high likelihood that there will be a general progressive pattern
over that region with a high amplitude upper level ridge building
over the mainland part of the state which will usher in warmer
temperatures. This ridge looks to get displaced later in the week
by a trough and hence the progressive pattern. The big
uncertainty remains the timing of these features as models have
not been consistent with one another or even with themselves on a
run-to-run basis. So what does all this mean for the sensible
weather next week? A warm up for the middle of the week with a
chance of precipitation. Precipitation type may be mixed for
inland areas in both Southwest and Southcentral Alaska mid-week so
that will be something to keep an eye on.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storms: 173 175
Gales: 150 155 160 165 170 171 172 174 176-181 185 411-414 .

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...EZ


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