Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 221254
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 AM AKDT SAT OCT 22 2016
.ANALYSIS AND UPPER LEVELS...
The upper level low over the Southern Mainland last night has now
tracked southward into the Southern Gulf, leaving a weak and
elongated easterly progressing upper level wave over the Southern
Mainland in it`s wake. At the surface, a low tracking into the
eastern gulf continues to push showers along the Northern Gulf
coast and surrounding areas, as seen in current radar imagery.
Current observations are also showing the outflow winds
surrounding Prince William steadily increasing, as the pressure
gradient tightens with the approach of the low.
Out West, ridging over the central and eastern Bering Sea
combined with lower pressure over the Gulf, continues to produce
gusty northerly winds across much of Southwest Alaska and Bristol
Bay. Further west, a front associated with a North Pacific low
southwest of Shemya continues to progress eastward into the
Central Bering and Aleutians today. Current observations are
showing that this system is currently bringing gusty southerly
winds, a few lightning strikes southeast of Shemya, and some
warmer temperatures to the area.
Models remain in good agreement through the much of the short
term, with some minor discrepancies regarding the strength and
placement of the low west of Shemya Sunday night. The High-Res
NAM was used in the east, mainly for more detailed winds and for
the timing of the outflow winds. Whereas out west, the GFS20 was
utilized out west.
VFR conditions will prevail throughout the day with SKC conditions
developing early this morning. Gusty northerly winds of 25 to 30
kts are expected throughout the day and should gradually weaken
starting late this afternoon. By midnight, winds will likely be
less than 10 kt.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The main focus for this package will be colder temperatures and
gusty winds, especially for favored gap locations along the north
gulf coast. Snow for this event is wrapped up with only cloud
cover leftover from this disturbance along with arctic air
filtering down through the Alaska Range. This arctic air and high
pressure inland will help drive outflow winds through the
Matanuska Valley, Seward, Whittier, and Valdez, among other areas.
Winds will peak in this afternoon and slowly diminish in
intensity through Sunday. As the winds taper off Sunday, cold air
will slightly moderate as lack of cloud cover allows for
insolation and warming of the low levels. Still expect
temperatures a little below normal for this time of year.
.SHORT TERM FORECAST SOUTHWEST ALASKA...
The upper ridge nudges across the Southwest today and stalls on
Sunday with the ridge centering over Bristol Bay into Monday
morning bringing clear skies across the region. Winds are
expected to gust along the western Alaska and Aleutian Ranges
through this afternoon and then taper off as the surface ridge
moves inland from the Bering. Subsidence along the periphery of
the ridge sinks colder air to the surface tonight, dropping
temperatures into the single digits and teens across the eastern
areas of the Kuskokwim Valley and Bristol Bay.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
The jet stream pushes a strong storm system across Shemya today bringing
max gale winds with storm force gusts and heavy rain along the
boundary. The front moves into the Pribilof Islands late this
afternoon with the southern extent of the boundary making it to
the easter Aleutians this evening. Northerly flow across the
Alaska Peninsula switches around to the south by tonight as the
front slides east. Gusty conditions are expected to strongest
along the western side of the peninsula as the surface becomes
stationary over the Southwest. Another system spins up rapidly
over the Kamchatka Peninsula late Sunday, potentially bringing
storm force winds across the western Bering and Aleutians late
Sunday into Monday.
.LONG TERM FORECAST (Days 3 through 7)...
The Southcentral region has an upper level ridge moving into the
region. This results in northerly offshore flow accompanied by
colder air filtering into the region through the upcoming midweek.
By Wednesday the ridge moves eastward allowing southwesterly flow
with warmer temperatures to advect into the Southcentral region.
Meanwhile, the Bering Sea has several low pressure systems
tracking from the south to north direction before exiting into the
Eastern Siberian region. These systems progressively become more
stronger with each passing storm. By Monday afternoon the GFS has
a 971 mb low tracking across the Western Aleutians before rapidly
intensifying to a 959 mb storm force low located in the central
Bering by Monday evening. As this system moves farther north look
for hurricane force southwesterly winds to develop just southwest
of Saint Matthew Island by Tuesday morning. This system brings
widespread rain/stratus with warmer temperatures to the Bering
through the upcoming midweek time-frame. By Wednesday this systems
exits the region across the Eastern Siberian region into the
Chukchi Sea. Therefore, the Bering/Aleutians will be under a
showery weather regime through rest of next week.
The models have been struggling with this major Bering Storm with
the ECMWF moving this system faster. While the GFS has been
stronger with this system, and slower. The intensity of these
systems between models has ranged from 20 to 30 millibars but has
become closer in there differences with each model run. The GFS
was the preferred model of choice in the long term time-period.
This system remains under close scrutiny for the possible weather
impacts as it tracks through the Bering.
SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH