Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 201221
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
421 AM AKDT Mon Mar 20 2017
.ANALYSIS AND UPPER LEVELS...
A blocking upper level ridge remains in place over much of the
Bering Sea. East of the ridge is a weakening upper level low over
the northwestern Gulf, and to the west is another upper level low
southwest of the Western Aleutians. More active weather persists
over the Northern Gulf, as the upper low and weakening surface low
remain in place over the Northwestern Gulf. Widespread snow and
snow showers continue to spread accumulating snow across much of
the eastern Kenai Peninsula and Northern Gulf coast, along with a
few passing showers over the western kenai Peninsula and Cook
Inlet. Relatively dry conditions were evident across the remainder
of the mainland.
The low southwest of the Western Aleutians and the weak front
associated with it stretching over the Central and Western
Aleutians produced gusty easterly winds and cloudy conditions
across the aforementioned areas.
Models overall remain in good agreement through the short term
forecast. The one caveat to that, is that the models continue to
struggle with the placement of the now weakening low center over
the Northwestern Gulf. These small differences however have not
led to any major uncertainties in the forecast or impacts, but
have led to prolonged snow showers over the areas surrounding the
Northern Gulf and Prince William Sound. GFS and NAM were both the
preferred solutions for this forecast package.
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level trough that remains over SouthCentral Alaska with
a cut off low just south of Seward will continue to drive the
weather around the area the next few days. As long as this low is
around the complex low in the northern Gulf will persist and bring
bands of snow showers along the coast. Inland areas will see no
more than just some cloud cover today with snow showers not
expected to make it across the mountains. As the upper level low
weakens overnight into Tuesday flow will remain light over the
Susitna Valley southward over Cook Inlet but be southerly over
Prince William Sound which will keep some snow showers in that
area. As the low edges farther eastward mid week it may bring in
some gusty northerly winds into the Susitna Valley and Cook Inlet
region behind it.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The pattern will remain largely unchanged through the middle of
the week as the strong ridge over the eastern Bering keeps dry
northerly flow focused over the southwest mainland. Winds will
continue to follow a diurnal curve characterized by gustier
conditions during the afternoon as daytime heating promotes
increased mixing. Temperatures will slowly moderate but remain
below seasonal normals through Wednesday, with overnight lows
continuing to approach zero beneath mostly clear skies.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure will continue to dominate the eastern Bering through
Wednesday, maintaining generally quiet conditions and a prolonged
period of abundant sunshine from Dutch Harbor and the Pribilof
Islands to the Akpen. The western half of the Bering will continue
to see rain and Small Craft Advisory conditions as a series of
relatively weak fronts move over the Western/Central Aleutians
and slowly dissipate.
.LONG TERM FORECAST (Days 3 through 7)...
The southern mainland continues under dry conditions through the
extended forecast as ridging dominates over the central and
eastern Bering. A slow warming trend can be expected during the
next week as the polar jet weakens along the western coast. The
most active weather will focus in the western Bering and Aleutians
as a parent low near the Kamchatka Peninsula moves several fronts
up from the Pacific. Snow showers are also prevail over the gulf
as a weaker surface low becomes better organized mid week due to a
strong upper level wave, progged to dive from the arctic, re-
invigorates the weakening low. The forcing from this upper wave
will also bring gustier north flow, especially along north to
south oriented gaps.
Models are in good agreement with the general synoptic pattern
through next Saturday; therefore a general blend of the
operational models/ensembles was used for updates. The upper level
ridge currently over the Bering breaks down mid week; however,
ridging re-amplifies in the same region as the subtropical jet
pushes an organized low into the far western Bering late Thursday.
This low moves a warm front into the central Bering and eastern
Aleutians bringing rain and gusty gales for the end to the week.
MARINE...Heavy Freezing Spray...121 127.
SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB