Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 301246
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKDT MON MAY 30 2016
.ANALYSIS AND UPPER LEVELS...
The mid-level high pressure system that has been entrenched over
the mainland for the past few days is beginning to retrograde to
the west, allowing a shift in the pattern for mainland Alaska.
Broad northerly flow on the eastern side of this high has brought
dry air and warm temperatures to the mainland over the past
several days. This is being enhanced by an upper level jet streak
that will move southward over the Southwest region. The beginning
of a series of stout easterly waves initiated showers and
thunderstorms yesterday afternoon and evening across nearly all of
Southcentral and parts of Bristol Bay in Southwest Alaska. Radar
shows that some of this shower activity has held together or
even increased through the night, given good dynamics aloft.
Further west, the pattern continues to be dominated by the upper
level high centered just north of the Bering Strait. A
strengthening low with widespread rain and gale- force winds is
approaching the Central Aleutians, but most of the Bering and Gulf
coast regions are being affected by marine stratus, as is evident
on visible satellite this morning.
Model agreement was fairly high this morning and so confidence in
the short term forecast is high.
The stout upper disturbance over the Interior of the state will
push across Southwest Alaska today and then west across the
central Bering tonight on the south side of the upper high and
north side of the low over the Central Aleutians. This disturbance
will also leave a mid-level boundary extending back to the east
into the northern Gulf of Alaska, which will be the next wave to
impact Southcentral Tuesday. Easterly waves will continue to push
across Southcentral through mid-week, but may begin to encounter
resistance over Southwest by ridging moving in from the north.
The low reaching near the Central Aleutians later tonight will
remain nearly stationary through Tuesday night while weakening
before dropping south into the North Pacific Wednesday.
Thunderstorm coverage will be the big question today as easterly
waves move across Southwest Alaska. The most likely areas to see
at least a storm or two are from the Copper River Basin west to
the Kuskokwim Delta, including the Susitna Valley, western Kenai
Peninsula, Alaska Range, and Middle Kuskokwim Valley. For now have
opted to go no higher than an LAL of 2 but there is potential for
some areas to see a little more organized coverage. Temperatures
and humidity values will moderate a bit from over the weekend with
the lack of strong northerly flow over the state.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Unstable air will remain over most of south central Alaska today
as the upper level low and associated strong short-wave slowly
slide west. It will be a little more stable today than it was on
Sunday, but some thunderstorms are still possible...mainly over
the Copper River and Susitna valleys. Conditions will stabilize
tonight as the upper low moves into southwest Alaska and the ridge
to the north nudges into the area. The area will then settle into
a pattern with a ridge to the north and a trough to the south for
Tuesday and Tuesday night. This will keep things mainly dry,
except for some diurnal convection over the mountains and some
showers along the eastern Kenai peninsula.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A set of easterly waves pushing through today will bring showers
and a few thunderstorms to areas from the Alaska Range west
through the Kuskokwim Delta this afternoon and evening.
Afterwards, broad cyclonic flow aloft on Tuesday will keep a
chance of showers to the Kuskokwim Delta and Bristol Bay, while
sunny and warm weather begins to return to the Kuskokwim Valley.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The gale-force low moving through the Aleutians will bring gusty
winds and rain to the region through Monday when it will begin to
dissipate over the Southern Bering through mid-week. To the west
of this low, northerly flow and cold air advection will allow for
persistent fog/stratus that has developed over the western
Bering/Aleutians to begin to diminish.
.LONG TERM FORECAST (Tuesday through Saturday)...
The pattern heading into the middle of the week shifts toward
low pressure across the Gulf and ridging to the west. The Bering
will trend toward a drier and more stable environment from mid-week
into next weekend. Meanwhile, low pressure across the gulf advects
moisture across the southern mainland through the end of the week
bringing increased cloud cover and rain chances. After a
relatively dry Wednesday, a deformation zone sets up near the
Alaska range as another low pressure system digs toward the
eastern Beaufort sea coast on Thursday. This combined with several
upper level shortwaves moving around systems will initiate
convective diurnal showers through the weekend. Models are in good
agreement on this synoptic change, however, there are differences
in handling multiple upper level disturbances from the two
dominant lows. The NAM was used to handle the transition into
Wednesday and then switched to the ECMWF along with some of the
06Z GEFS MEAN in the extended range, which provided the best
MARINE...Gales...165 170 172-175.
SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC