Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 290031
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 PM AKDT THU JUL 28 2016
.ANALYSIS AND UPPER LEVELS...
There are 3 significant features present across the state today.
The first and strongest is an Arctic Low over the Beaufort Sea.
The next is an upper level ridge sliding over the Western Bering.
And finally, our pesky vertically-stacked low continues to meander
over the northern Gulf of AK. A front associated with the Gulf low
pushed through the Cook Inlet region overnight bringing moderate
to heavy rain along the coast and light rain inland. The front is
now hung up in the Susitna Valley and is being stretched down
through the southern Cook Inlet. Another piece of energy is
swinging around the center of the low and will bring another round
of rain and gusty winds from Cordova into the Prince William
The Arctic Low is slinging a trough through Southwest AK. This is
helping to trigger some showers over the YK-Delta. With some
sunshine helping to create instability east of of the trough, we
still expect some isolated thunderstorms to initiate over the AK
and Aleutian Ranges this afternoon-evening.
The ridge over the Bering continues to keep abundant marine
stratus and fog in the area. The ridge axis has passed to the east
of Shemya. This has allowed some weak southwest winds to bring a
bit more mixing and help to clear out some of the fog and low
stratus. But this looks to stay confined to the extreme Western
Models are in generally good agreement through the short term.
This is lending to moderate to high forecast confidence. Timing
for the shortwave from the northwest late tonight into tomorrow
morning is consistent among the members. There is some debate in how
much instability can build in with the slow clearing this
afternoon. Thus, we are contemplating removing any mention of
thunderstorms from the Talkeetna Mountains and eastern slopes of
the AK Range. Winds across Southcentral could prove tricky this
afternoon and evening as well. With limited clearing, southeast
winds might not make much of an appearance across south and west
Anchorage and the Matanuska Valley.
Beyond that...models agree in some weak, flat ridging into
Saturday as the stronger trough drops down from the Bering Strait.
But by Sunday, all bets are off as to where the closed low will
develop on the southern end of that trough. Forecast confidence is
low Sun into Mon as some solutions would bring very wet conditions
into the southern half of the state, while otherwise would allow
much of the area to remain mostly dry.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The low in the Gulf sits near Middleton Island and is pulling in
moisture over Southcentral Alaska. With the atmosphere already
unstable due to the low also bringing in colder air aloft over
Southcentral, and afternoon temperatures in the upper 60s,
isolated thunderstorms have developed around the Talkeetna
Mountains and surrounding valleys. These thunderstorms look to
last into the evening until temperatures drop and more widespread
cloud cover comes in from a shortwave approaching from the west.
The Gulf low will push off to the southeast overnight and ridging
will move in over the area behind both of these features on
Friday. The ridging will bring in somewhat more fair conditions
but looks to be weak and will not completely inhibit rain,
especially over the mountains into early Saturday.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The showery regime will linger only a few more hours before a new
pattern takes hold. Southwesterly flow will spread over the area
late tonight and tomorrow, which will bring a chance of rain,
mainly to the northern portions of the mainland. Friday night into
Saturday a front will drop down from the north, and will spread
plentiful rain from west to east across the mainland. Temperatures
will be average for this time of year while winds remain light
from the southwest.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Marine layer stratus and fog encompass the majority of the Bering
Sea. As a weak trough progresses across the central Bering,
drizzle will accompany the low ceilings. A weak disturbance
traverses the Western Aleutians Friday evening before petering out
on Saturday. A front drops in from the north on Saturday,
spreading rain over the central and eastern Bering Sea. Winds will
remain generally light from the southwest until the front
approaches, then will increase.
.LONG TERM FORECAST (Days 3 through 7)...
Sunday through Wednesday the synoptic pattern will be transitory
as a closed low traverses from the Bering to Gulf with a ridge
amplifying in it`s wake. Models are trending toward better
agreement in this solution, however they still differ in the speed
of the eastward progression of the low. Only minor adjustments
were made to the extended range forecast using a blended approach
including all operational models beyond Monday.
SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML