Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 211232
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 AM AKDT SAT MAY 21 2016
.ANALYSIS AND UPPER LEVELS...
A cold core upper level low sits relatively stationary over the
Northern Bering with ridging to the east out over the Gulf.
Between these two features a quickly moving low has moved in over
Southwest Alaska from the North Pacific and has brought rain to
the area with its front draping across the Southcentral. The
pressure gradient between this low and the ridging to the east is
bringing strong gap winds to the Southcentral. Another low south
of the Central Aleutians is tracking east bringing more rain to
The models are in good synoptic agreement through the mid term
with only some timing issues with a North Pacific low approaching
the Western Aleutians Monday. However, on a mesoscale they are
struggling to handle the winds in the Southcentral lowering
confidence in how strong the winds will get and how long they will
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The main weather focus through the weekend surrounds developing
westerly flow across the Gulf, Cook Inlet and Shelikof Strait.
The southern mainland will see a reprieve from the gusty winds
that developed on Friday as ridging across the northeast Gulf
rapidly weakens this morning. Light rain will continue to develop
through Sunday night as an upper level trough moves overhead today
followed by the parent low tracking across from the Bering.
Westerly flow develops across the southwestern Gulf this morning
as ridging builds across the southwest mainland. Winds shift
across Shelikof Strait and southern Cook Inlet by the afternoon.
Zonal flow sets up across the Gulf tonight between low pressure
over the mainland and ridging in the Pacific. Gusty west flow
brings widespread small craft winds to area marines with gales
across the western Gulf into early Monday morning.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Rainfall across the southwest mainland will continue to taper off
from west to east throughout the day today. A brief reprieve in
rainfall will be seen across Southwest Alaska late this afternoon
through this evening but a low currently situated just to the
south of Adak will quickly push across the Bering Sea and move
inland near the Kuskokwim Delta and bring the return of rain to
the region tonight. The bulk of the rain is expected to start
falling after midnight tonight with rain continuing through Sunday
evening before once again tapering off from west to east during
the overnight hours on Sunday/Monday morning. Another brief
reprieve will be seen Monday morning but a weak shortwave
traversing the zonal upper level flow will bring rain chances back
to Southwest Alaska once again.
Temperatures will remain on the cool side and quite possibly
below normal through the weekend as a cold core upper level low
remains just to the west of the southwest mainland. Looking at the
00Z and 12Z RAOBS from PABE and PAKN, a cooling trend in the lower
levels has been observed as the cold air rotates around this upper
level low and moves across the region. This cooling trend aloft
has been and will contribute to the cooler weather currently being
observed. During the breaks in rainfall, patchy to areas of fog
will be possible with fairly light winds and well saturated
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A fairly unsettled weather pattern will continue across the Bering
Sea through the weekend with a longwave trough encompassing much
of the Bering Sea. Within this trough lies several potent upper
level lows and shortwaves which will continue to move through the
Bering Sea and bring rain to much of the region. The most
impressive surface feature is a low currently located just to the
south of Adak. This low is expected to quickly push northwest
toward Southwest Alaska during the day today and bring small craft
winds and seas to the central and eastern Aleutians. A nice slug
of moisture associated with this system will bring some decent
rainfall to Adak, Atka and Unalaska throughout the day.
The pattern begins to break down on Monday as the upper level
flow becomes more zonal and allows weak surface high pressure to
build across the southern Bering Sea. Expect fog to form along the
eastern Bering Sea during the morning hours today with the thicker
fog likely limited to northern portions of the Bering. By Sunday,
areas of fog will begin to develop over Bristol Bay and extreme
eastern portions of the Bering Sea which will mix out during the
afternoon hours and re-develop with the loss of daytime heating
and stabilization of the sfc layer.
.LONG TERM FORECAST (Days 3 through 7)...
Starting Sunday night, an upper level trough moving through the
South Mainland will bring widespread rain and clouds to the area
into early next week. Cold air will also filter down from the
Bering Sea behind the trough, keeping temperatures at or below
normal into Tuesday. Over the Bering, weak ridging will keep
significant systems from approaching the area through early next
week, leaving westerly winds below small craft and otherwise quiet
weather. By the middle of next week the models begin to diverge
significantly with an upper level trough diving out of Siberia
into the Bering. There are some major differences with the track
of a Bering low and an associated front, limiting the forecast
confidence throughout the area to low.
SYNOPSIS AND MODEL DISCUSSION...dk
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...mc