Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 190152
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 PM AKST Mon Feb 18 2019

.ANALYSIS AND UPPER LEVELS...
A front associated with a weakening, vertically stacked low over
Bristol Bay continues to rapidly push eastward towards the
eastern Gulf and ALCAN border. An upper level trough over
mainland Alaska is slowing moving eastward. Cold air wrapping
around the backside of the low is causing some cumulus clouds over
the Bering this afternoon. Southwest flow is moving into Bristol
Bay and Southwest Alaska, as well as a few snow showers over the
K-Delta. Light snow showers have also been observed across
Southcentral, along with a mix of rain/snow along the coastal
regions. One key weather feature to keep an eye on is quick moving
low center developing in the North Pacific south of Adak.

&&

.MODEL DISCUSSION (through Wednesday afternoon)...
Numerical models are in very good synoptic agreement through
Wednesday afternoon. All have similar handling of the outflow
pattern across the North Gulf on Tuesday and the developing low
and surface front moving into the eastern Bering Sea Wednesday.
The GFS will be used overall in the western domain and the higher
resolution NAMNEST in the east capture outflow winds.

&&

.AVIATION...

PANC... MVFR/IFR conditions possible in snow showers until after
trough passage overnight. North winds should develop on Tuesday
and bring drying and VFR conditions.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
(Mon night through Wed)

The main items of interest in the short term are refreeze
potential tonight as temperatures drop back into the upper teens
to lower 20s for most locations across the Anchorage Bowl.
Then, strong northerly winds will develop for Tuesday as an area
of low pressure crosses southwest Alaska tonight and into the Gulf
by morning, reaching the Yakutat area by Tuesday evening.

As this occurs, a brief ridge of high pressure will build across
Southcentral, with it being centered north of Broad Pass. This in
turn helps promote a tight pressure gradient along the eastern
slopes of the mountain ranges, with the winds increasing for the
Prince William Sound region, Whittier, Thompson Pass/Keystone
Canyon, and the Copper River Delta. For these locations look for
peak wind gusts to top out in the 40 to 50 mph range. As such, we
hoisted a Winter Weather Advisory for this section of the
Richardson Highway for Tuesday morning through Wednesday morning.
Visibilities could drop to a half mile or less in blowing/drifting
snow through Thompson Pass.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3...Mon
night through Thu)...

Low pressure crossing over to the gulf tonight will bring snow
along the Kuskokwim Valley and Bristol Bay areas east of
Dillingham and then taper off toward Tuesday morning. A ridge
builds across the Southwest in the wake of the front which
supports fog development across the Alaska Peninsula and the
Southwest as low level moisture is abundant and temperatures cool
to dewpoint values overnight.

The next front moves across the Alaska Peninsula Tuesday
morning. Precipitation will likely start out as snow along the
boundary, however the warm core system is expected to warm the
column enough to change over to rain. The boundary pushes to the
west coast during the afternoon, however the ridge just inland
shunts its progression. Gusty southeasterly winds are expected to
increase along the front with snow and blowing snow, especially
further north, for Wednesday night.

On Wednesday night into Thursday, a strong short wave develops
along the base of the upper trough and swings north which brings
another frontal push which is expected to bring widespread snow
across the area. We will be monitoring this closely for potential
advisory (6") level accumulations.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3...Mon
night through Thu)...

Low pressure keeps an unsettled pattern over the Bering through
Thursday. While low pressure across the eastern waters exits
tonight, another track north along the west Bering. The next
North Pacific storm moves up to the Central Aleutians tonight and
continues on a northward track. This system will bring rain and
snow across the Aleutians tonight along with gusty easterly gales.
The storm picks up northward momentum Tuesday morning which
swings the front at a fast pace to the northern waters making
blowing snow issues for Pribilof Islands fairly brief. The
following system enters late Wednesday across the Western
Bering...bringing blowing snow possibilities across the western
Aleutian Chain as the cold core center passes close to Shemya.

&&

.MARINE (Days 3 through 5...Thu through Sat)... A very active
storm track continues across the Western Bering Thursday through
Saturday. Models have come into agreement that a mid-960 mb low
will move up the Western Bering on Thursday, bringing southerly
gale force winds through most of the Bering Sea. Another low
pressure system is expected to develop on its tail in the Northern
Pacific, crossing the Aleutians and moving into the Bering on
Friday afternoon. Winds with this next system are expected to
remain near max gale force, but northwesterly winds on the western
side of the system may increase to storms by Saturday.

Of note in the Gulf of Alaska, high pressure will build in behind
the low expected to move into Prince William Sound on Thursday.
This has the potential to cause strong northwesterly outflow
winds across the Western Gulf and through the Barren Islands
Thursday afternoon. Right now winds are expected to peak below
storm force but this bears watching as the two systems develop.

&&

.LONG TERM FORECAST (Days 3 through 7...Thu through Mon)... The
westerly storm track will continue across the mainland on
Wednesday and Thursday before a ridge builds in over the eastern
mainland on Friday. The ridge will shift the weekend`s storms to
a more south to north track through the Bering Sea. The storm that
moves through the mainland on Weds and into the Prince William
Sound on Thurs will bring snow across the region, with the
potential for 6 inches or more through the Mat-Su Valley. By
Friday, the ridge will be settling into place, which means that
any weekend potential for precipitation will be kept from the
Kuskokwim Mountains westward.

Although there is certainty in the ridge building over the
mainland through the weekend causing a change in the general storm
track, some uncertainty still exists in the strength of the ridge.
This could make the difference in whether some precipitation makes
it further inland Saturday and Sunday, or whether it is mainly
held to the coast. Regardless, it does look like an influx of warm
air is likely, so precip type for the western mainland will
likely be a forecast challenge as we move into early next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Coastal Flood Advisory: 161
 Winter Weather Advisory: 131
MARINE...Gale Warning: 120 129 130-132 138 351-352, 150-170 176 179-185
411 414.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AH/RMC
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
MARINE/LONG TERM...LF


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