Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 300053
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
453 PM AKDT Mon May 29 2017

.ANALYSIS AND UPPER LEVELS...
There is an upper level low over southern Alaska moving fairly
rapidly to the north. The flow is fairly strongly cyclonic with a
decent vort-max over the Cook inlet/Susitna valley area. There is
some shower activity over much of southern Alaska. There is an
upper level ridge behind this low over the Gulf of Alaska, which
bends northward along the west coast of the state. There is a
fairly large upper low over much of the Bering Sea, centered just
north of the western Aleutians. A nearly stationary front
associated with this low is over the central Bering extending to
just west of Umnak island.

&&

.MODEL DISCUSSION...
The numerical models are in fairly good agreement during the short
term portion of the forecast. There are still some differences in
timing and location of showers/drying in the first 24 hours.
Forecast confidence is thus near to slightly below normal.

&&

.AVIATION...
PANC...VFR conditions will persist. Breezy southerly winds will
diminish this evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

A dynamic closed upper low over the region is finally lifting
northward towards interior Alaska this evening. Instability
showers are encompassing most of the inland areas, especially
regions along and west of the Chugach and Talkeetna Mountains.
Enhanced Turnagain convergence is enhancing local showers around
Anchorage as well, but these should rapidly diminish during the
later evening hours. Showers will linger the longest across the
Northern Susitna Valley where favorable flow behind the departing
upper low will keep upslope precipitation through the morning
hours tomorrow.

Tuesday and Wednesday will see building heights aloft and warming
temperatures as the pressure gradient gradually becomes weakly
offshore. With clearing skies and warming temperatures aloft (850
hpa temperatures get close to 7-10 C by Thu, the warmest of the
year at that level), expect each successive day through Thursday
to be warmer region wide. Wednesday and Thursday will be the first
above average temperature days in quite a while. Diurnal sea
breezes should be in place along the coast, but the offshore
pressure gradient will delay them somewhat. Inland areas like
Anchorage may flirt with some local 70 degree temperatures by
Thursday given the favorable gradient.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The upper level trough over Southwest Alaska will lift away to the
northeast tonight with an upper level ridge building in behind it.
The amplifying ridge will end showers overnight with warm and dry
weather prevailing Tuesday through Thursday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The broad vertically stacked low currently centered over the
southwestern Bering will track gradually east-southeast to cross
the central Aleutians Tuesday night and Wednesday and then arrive
south of the Alaska Peninsula Thursday. An associated frontal
system will progress slowly into the central Bering through
midweek while a developing frontal wave to the south lifts another
piece of the front into the eastern Aleutians Tuesday night. The
front will then pivot east spreading more of the front north to
the Alaska Peninsula Wednesday and Wednesday night as the upper
low speeds up and crosses by to the south of it.

&&

.FIRE WEATHER...
The ridging building across southern Alaska will bring a
significant warming and drying trend starting Tuesday and
continuing through Thursday with minimum relative humidities
dropping into the 20s and high temperatures climbing into the 60s
to low 70s. Following this warm and dry spell, the upper level
ridge will shift north over western and interior Alaska with an
upper level low becoming centered in the Southern Gulf. This
upper level progression will open Southern Alaska to easterly
waves moving in from the Yukon Territory towards the end of the
week. The combination of this incoming mid moisture, instability
and the warmest air mass of the year so far will bring the
potential for isolated to possibly scattered thunderstorms Friday
and Saturday. While confidence is moderate in this general pattern
progression, continued large run to run model variations in the
location of the upper level features keeps uncertain high
regarding the location most likely for thunderstorms to form.

&&

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

There is high uncertainty in the long range forecast beginning on
Friday as models differ with solutions on a low across the Gulf
of Alaska. They are trending toward a similar solution that the
southern mainland and gulf will see increasing rain chances
through the extended forecast into Monday as a broad trough moves
several low pressure systems from the North Pacific to the gulf.
To the west, a less organized pattern is anticipated with weak
ridging over the central Bering expected to shift as multiple
disturbances move through the flow from the Northeast Pacific and
eastern Russia. The inherited forecast was kept intact due to the
lack of model run consistency.


&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

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


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