Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 281230
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
430 AM AKDT WED SEP 28 2016
.ANALYSIS AND UPPER LEVELS...
There is a fast-moving, deamplifying shortwave trough transiting
the northern Bering Sea this morning with its associated front
moving into the Kuskokwim Delta. Shortwave ridging ahead of the
trough is moving east into Southern Alaska this morning with
clearing skies and efficient radiational cooling. Farther west
toward Kamchatka and across the north-central Pacific Ocean, a
complex area of separate upper troughs and surface lows is
beginning to amalgamate. Eventually this will allow for broad warm
air advection and increasing southerly winds to move into the
Bering Sea today and tomorrow before a stronger low moves into the
eastern Bering Sea Friday.
The numerical models are in excellent agreement with the large
scale synoptic pattern through the weekend. They are in overall
good agreement with the timing of a warm front moving through the
Bering into Thursday, but they still remain in lesser agreement
with a strong potential storm force low moving into the eastern
Bering Sea Friday. However, they are converging on a solution and,
as a whole, are depicting a similar impact. As a result, forecast
confidence is very high with this forecast package as the small
uncertainty does not lead to dramatic potential errors.
PANC...VFR conditions will continue today with light winds. There
is a remote chance for a brief period of fog this morning but
confidence is low and therefore not added to the TAF.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The Anchorage sounding this morning reveals quite dry conditions
throughout the depth of the atmosphere. This dry air, along with
light mixing winds is limiting fog formation across much of
Southcentral this morning. As a result, temperatures have fallen
quite rapidly overnight, with frost forming in portions of the
Anchorage Bowl this morning. Another dry pleasant day is expected
across much of Southcentral as an upper level ridge centered near
the eastern Aleutians and southern Pacific slowly pushes eastward
into Southcentral and amplifies. Meanwhile, an upper level trough
sliding from west to east north of the Alaska Range could bring in
some higher clouds this afternoon. However, this trough will push
quickly to the east, and another round of cooler temperatures is
expected across the area this evening.
.SHORT TERM FORECAST SOUTHWEST ALASKA...
Upper and surface ridging along the Alaska and Aleutian Ranges of
southwestern Alaska gets shunted east as a fast-moving trough
brings areas of light rain to northern areas mainly north of
Bristol Bay through this afternoon. Upper ridging rapidly
amplifies behind this trough and brings clearing skies, with
strong nighttime surface inversions in the valleys presenting a
good chance of at least some patchy fog.
This amplified ridge slides east with deep southerly flow
developing along the Kuskokwim Delta coast by Thursday night, with
the first in a series of warm fronts likely to bring some wind and
rain mainly west of Bethel.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
The combination of amplifying ridging over the Bristol Bay and
Alaska Peninsula region along with an upper low moving into the
Western Bering from Russia will create a strengthening and very
active jet stream later today through the remainder of the week
across the region. A series of waves and associated warm fronts will
push north from the North Pacific into the Bering and Aleutians
beginning this evening out ahead of the main surface cold front.
This cold front will reach the Western Aleutians tonight and then
and then slowly move east as a gale-force low forms along this
front near the Central Aleutians Thursday into Thursday night
while impacting the southern Bering region and the Eastern
Aleutians and the southern Alaska Peninsula.
.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.
SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC