Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 291230
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
430 AM AKDT FRI JUL 29 2016
.ANALYSIS AND UPPER LEVELS...
The primary weather features impacting the area today include the
vertically stacked low centered over the Gulf of Alaska and the
broad flat ridge over the Bering and Aleutians. An upper level
trough has closed to a weak low south of the Alaska Peninsula
while a strong low over the arctic low is tightening the west-
northwesterly upper level flow from Russia across the Bering
Strait and into Western Alaska. Clouds are streaming east into
mainland Alaska as shortwave troughs rotate around the south side
of the arctic low.
While models have slowed the trough dropping out of the northwest
this weekend substantially since yesterday (primarily due to it
cutting off into a closed low earlier and further west) they do
all seem to be on board with this new solution and are in good
agreement through Sunday. As we move into next week, models
remain in fair agreement which is a substantial improvement of the
large spread they had yesterday...so confidence is increasing in
the idea of a broad upper level low tracking from west to east
from Southwest Alaska and across the Gulf through the first half
of the week.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A much drier day is on tap for most of Southcentral today as the
low over the Gulf exits to the east and a flat ridge builds in
from the west. There is a very weak wave right out ahead of the
ridge, but it is not strong enough to generate any precip on its
own. Low level west to southwest flow, however, may lead to some
very light rain or sprinkles on the western slopes of mountains as
this moves through. At a minimum, expect clouds to hold in along
the mountains with increasing sunshine as you move away from the
mountains. The one big exception to all of this is the very
northern tier of the forecast area, along the Alaska Range and
northern Susitna Valley and Copper Basin. Upper waves riding along
the top of the ridge will combine with upslope flow to produce a
cloudy and showery day. Precip will transition to steady stratiform
rain tonight as the air mass stabilizes and persist through Saturday.
Saturday looks mostly warm and dry for the rest of Southcentral,
although the persistent west to southwest flow and stable air
under the ridge may trap some clouds along the west sides of
mountains, especially along the east side of Prince William Sound.
A deep trough and associated surface front will approach from the
west Saturday Night with increasing clouds and rain beginning to
nudge in to western-most areas.
The other impact of the west to southwest flow will be a
persistent lee side trough from Shelikof Strait up to Cook Inlet.
Have trended stronger with winds along this corridor with solid
Small Craft Winds expected for much of the next two days. Some
of the wind will work its way up to the Susitna Valley as well.
A weak surface ridge over the Gulf combined will also produce
occasional gusty winds along Turnagain Arm into Anchorage, along
the Knik River Valley into Palmer, and along the Copper River.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level closed low remains parked over the Barrow region
with an associated trough extending southwestward through Eastern
Siberia towards the Kamchatka Peninsula region this morning.
A weak shortwave is moving through the Lower Kuskokwim Valley
producing periods of rain this morning. By Saturday midday, the
trough associated with the closed upper level low near Barrow will
be located through the Bering Strait extending southwestward into
the western Bering. This synoptic feature will be reflected at the
surface with a 1006 mb low positioned over the Y-K Delta region
with an associated weather front extending into the northern to
central Bering Sea. This will bring onshore southwesterly flow
with widespread rain moving from west to east across the Southwest
Alaska region through the weekend.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The main feature will continue to be the marine layer stratus/fog
through the majority of the Bering Sea. As the low pressure system
drops down from the north heading into Saturday, it will produce
light southwesterly flow throughout the Bering. By late Saturday
afternoon the low pressure system moves inland near Hooper Bay,
and high pressure over the Kamchatka Peninsula tracks into the
Bering. This ridging will continue to enhance the marine layer
stratus/fog through the weekend.
.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...JER
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD