Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 280003
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
403 PM AKDT TUE SEP 27 2016
.ANALYSIS AND UPPER LEVELS...
There is an upper level ridge over western Alaska that is moving
towards the east. A weak upper level trough over Southcentral
Alaska is also moving east with the western Alaska ridge building
behind it. There is a fairly robust positively tilted gale force
front over the central Bering Sea. This front is associated with a
large and deep upper low that is centered over northeast Russia.
The numerical models are in good agreement through the short term
portion of the forecast (Thursday afternoon). The models begin to
differ with a low south of the western Aleutians on Thursday
afternoon, with the ECMWF much weaker and further south. Forecast
confidence is thus a bit above normal today.
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Mostly clear and dry conditions will persist over Southcentral
Alaska through the end of the week as a amplifying North Pacific
ridge builds over the area this evening from the west. The only
exception to these clear and dry conditions would be a small
window of mid-to-high level clouds moving in from the west
Wednesday morning to early afternoon, as a weak upper level wave
tracks over the area.
Colder overnight temperatures are expected across Southcentral
overnight tonight and overnight Wednesday, with mostly clear
skies and weak/dry offshore flow. Outflow winds through the gaps
surrounding Prince William Sound and the Northern Gulf Coast (Valdez,
Whittier/Portage, Seward, and Copper River Delta areas.) will pick
up Wednesday night and persist through Thursday night. This is due
to high pressure and cooler temperatures setting up over the
inland areas, and tightening the gradient between the lower
pressure and warmer sea surface temperatures over the Gulf and
Prince William Sound.
.SHORT TERM FORECAST SOUTHWEST ALASKA...
A trough out over the northern Bering will push through the
Kuskokwim Delta tonight and the remainder of southwest Alaska
Wednesday morning bringing rain to the area. Wednesday afternoon
ridging will move in over the area from the west and last through
Thursday which will help with fog formation during night time
hours. Late Thursday a new system pushes in from the south
bringing rain and strong winds to coastal areas. On Friday the
rain will push further inland as the parent low moves into the
.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
High pressure will dominate much of the Bering and Aleutians
through much of Wednesday before a shortwave pushes north across
the Central Aleutians Wednesday evening. Following behind that
shortwave is a much stronger system that will bring its front
across the Central Aleutians late Thursday and to the Alaska
Peninsula by Friday morning. This system will be characterized by
rain and strong winds that will impact much of the Bering and
Aleutians with the strongest winds over the eastern Bering on
.LONG TERM FORECAST (Days 3 through 7)...
The extended term will begin on Thursday night with a high
amplitude ridge extending over the center of the state from the
subtropical Pacific, keeping the southern mainland precipitation
free beneath mostly clear skies towards the end of the work week.
Rain will return to Southwest AK Friday night into Saturday as a
front associated with a low moving into the Bering Sea arrives
along the coast and pushes inland. Forecast confidence then
quickly begins to decrease during the weekend regarding the
evolution of the Bering system and how it interacts with the ridge
in place over the mainland. The current forecast reflects a blend
of ensemble guidance which has a general consensus of weakening
the front over the southwestern gulf and shunting the remaining
energy towards the southeast as it encounters and eventually
bisects the Pacific ridge, displacing the mainland high to the
north but still keeping weak high pressure over the southern
mainland through early next week. This would have the net effect
of keeping Southcentral AK mainly dry throughout the extended
period, with temperatures hovering near seasonal normal values and
dipping to near freezing at night. Meanwhile, the Bering looks to
remain in a more active pattern as various waves rotating around a
deep Siberian low bring sporadic windy and rainy conditions
through early next week.
MARINE...GALE WARNING 172 173 174 175 176 181 185 411 413.
SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK