Area Forecast Discussion
Issued by NWS Anchorage, AK

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697
FXAK68 PAFC 280033
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 PM AKDT Thu Jul 27 2017

.ANALYSIS AND UPPER LEVELS...

Water vapor imagery this morning shows an upper level low
spinning south of Kodiak Island, with a front just to the west of
this low. This front is doing little to mix out the wide swath of
stratus that is covering the Bering and keeping cloud ceilings low
especially in the Pribilofs. Meanwhile weak ridging aloft over
the mainland and north Gulf Coast, along with copious low level moisture
is supporting widespread fog and stratus across much of Southcentral.
Meanwhile to the east, an upper level wave is supporting widespread
showers across the eastern Copper River Basin.

&&

.MODEL DISCUSSION...

Models are in generally good agreement in the short term with the
upper low south of Kodiak Island pushing into the Gulf of Alaska,
while high pressure for the most part maintains its hold over the
Bering Sea. For Southcentral, high resolution models were favored
to best capture local effects and stratus coverage.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Fri and
Sat)...
A generally cloudy and slightly cooler than normal pattern will
persist for the next few days. The 2 primary features are a low
clipping the eastern Copper River Basin and another low diving
southward through the Gulf of AK. The first low is helping to
trigger some afternoon/evening thunderstorms across part of the
Copper River Basin. We are not expecting this to create
widespread lightning, but a few "garden-variety" storms will be
possible through the evening before dying off overnight. The Gulf
low has left weak high pressure over the southern mainland. This
means some subsidence aloft and generally weak flow. Thus, any
clouds that are lingering around now could stay around for the
next several days. It will also make for the potential for some
low stratus and fog, especially near open water sources, come Fri
morning.

There should be enough moisture and stability in the column to
restrict thunderstorm development across the domain on Fri
afternoon/evening. However, showers along the mountains will still
be probable. The low in the Gulf starts to pivot back to the north
late Fri into Sat. This could bring enough energy up along the
north coast into Kodiak to make for a brief period of light rain
early Sat. But by Sat afternoon, weak offshore flow across much of
the mainland should help to increase the amount of sun making it
through the clouds. This sun should also lead to enough
instability for another round of isolated thunderstorms across the
AK Range, the Talkeetnas, and part of the Copper River Basin.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A frontal system along the west coast will push inland over the
Kuskokwim Delta this afternoon and evening and then continue
slowly east across Bristol Bay and Southwest Alaska tonight
through Friday. Isolated thunderstorms are possible out ahead of
the front through this evening over inland Southwest Alaska where
there has been more solar heating to combine with the moist and
unstable air mass in place. A trough will linger over Southwest
Alaska through Friday night with showery weather persisting until
a Bering shortwave swings by offshore and crosses the Alaska
Peninsula early Saturday morning. Upper level ridging will build
over the eastern Bering following the shortwave and then tilt east
into Southwest Alaska tapering showers off Saturday and Saturday
night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
West to southwesterly flow persists across the Bering as high
pressure remains in place over the Aleutians. A weak west to east
running frontal system stretch across the southern Bering will
continue to bring precipitation to that area with stratus and fog
covering much of the remainder of the Bering.

&&

.LONG TERM FORECAST (Days 3 through 7/Saturday night through
Thursday)...
The large scale pattern remains fairly persistent through the
extended forecast period. The strong blocking ridge centered
just south of the Western Aleutians looks like it will weaken
with persistent waves riding over top of it, tracking eastward
across the Bering Sea then dropping southward into a trough over
the Gulf of Alaska/Northeast Pacific. Model guidance differs in
some of the details of individual waves, but shows the same
general idea. Thus, generally speaking expect wet conditions
across the Bering Sea and into Southwest Alaska along with
continued areas of fog and stratus across the region.

Meanwhile, weak ridging will persist in the vicinity of
Southcentral. A steady stream of upper waves will pass in the
vicinity of Southcentral, but forcing looks weak. The lack of
strong forcing or strong flow creates quite a challenging
forecast. At this time scale it`s nearly impossible to forecast
the details of what any given day will be like in Southcentral.
Overall, we can say there will be a lot of "fair" days; not wet
or dry, not hot or cold, not cloudy or sunny - but somewhere in
between these dichotomies. There are indications the ridge will
break down late next week, with potential for storms to approach
Southcentral from both the west and south.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EN
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...SEB



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