Area Forecast Discussion
Issued by NWS Anchorage, AK

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328
FXAK68 PAFC 250104
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
504 PM AKDT Thu May 24 2018

.ANALYSIS AND UPPER LEVELS...
The upper level pattern is largely unchanged from previous days,
with an elongated trough spanning much of the North Pacific from
the western tip of the Aleutian chain to the eastern Gulf of
Alaska. Broad cyclonic flow associated with this feature is
supporting a showery regime across the Bering Sea and southern
mainland. A weak front is lifting north through the Gulf, helping
to enhance winds to Small Craft Advisory level over the coastal
waters and also aiding in the development of modest gap winds
through typically favored areas including Turnagain Arm. Showers
continue to be most widespread along the coast, with inland
convection remaining sporadic and following more of a diurnal
curve.

&&

.MODEL DISCUSSION...
Guidance is in generally good agreement through the weekend as the
low anchoring the North Pacific trough moves east from the Bering
into the Gulf of Alaska and allows upper level ridging to build in
across the Bering. There are some small differences with placement
and timing of an attendant surface low moving into the Gulf by
Saturday, so generally favored more of a GFS/NAM based solution by
Day 3 as the ECMWF has struggled with run to run consistency. GFS
also represents a good middle ground for another front moving into
the Bering late in the weekend.

&&

.AVIATION...
PANC...Gusty southeast winds will persist through late tonight and
then subside around 12z as the pressure gradient becomes more
favorable to down inlet flow out of Turnagain Arm. VFR conditions
will persist through the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Clouds and scattered showers will persist this evening from
Cordova west to Kodiak as a weak upper-level shortwave stretches
along the coast. A second surface low will develop just to the
east of Kodiak Island along the afore-mentioned decaying feature
later tonight. This system will push an occluded front along the
coast Friday, bringing yet another round of rainfall to coastal
locations through early Saturday. Lingering coastal showers will
diminish in coverage Saturday afternoon as the front dissolves
and a general offshore flow develops. Aside from a few scattered
showers over the mountains, inland valley locations should remain
mostly dry. A thermal trough dropping south from central Alaska
Saturday could help enhance the chance for showers and isolated
thunderstorms along the Talkeetna and Alaska ranges Saturday
afternoon.

Southeasterly gap winds will continue Thursday and Friday
afternoon and evening for Turnagain Arm, south and west
Anchorage, Knik River Valley, and Copper River Basin. These winds
will subside Saturday as a more offshore flow develops.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The upper level wave which brought steady rain to portions of the
Kuskokwim Valley and Kuskokwim Delta today will exit into the
Bering tonight. isolated to scattered showers elsewhere formed
under weak instability and little other forcing, so expect them
to dissipate pretty quickly this evening with loss of sunlight.
With some breaks in clouds, it will be another chilly night, with
temps dropping into the 30s in to lower 40s.

A very weak therm trough will set back up on Friday along the
Kuskokwim Valley down into interior Bristol Bay, right in between
weak upper waves coming in from opposite directions. With the
overall weak forcing expect just some isolated to scattered
diurnal convection. The potential for convection looks more
impressive on Saturday as a thermal trough strengthens from
interior Alaska down along the west side of the Alaska Range.
This will be the focus for showers and thunderstorms. Meanwhile,
as an upper ridge builds over the Bering Sea, cooler air will
advect southward out ahead of it along the Southwest coast. This
will lead to drier more stable conditions and chilly night-time
temperatures - perhaps dropping to near freezing. This airmass
will make a bit of progress eastward on Sunday, which should
confine any convective activity to right along the Alaska Range.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The weakening low over the southern Bering Sea will drop southward
into the North pacific tonight through Friday, with an upper
level ridge building in behind it. Cold advection down the front
side of the ridge will lead to gusty northerly winds over the
eastern Bering Sea and down to the southern Alaska Peninsula
beginning and continuing through much of the weekend. The upper
levels will remain progressive with a new storm system moving to
the western Aleutians Saturday night and continuing eastward
across the Bering Sea on Sunday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast beginning Sunday starts with a weakening
surface low over the eastern Gulf of Alaska being pushed east
into the Panhandle as an upper ridge builds in over the western
and central parts of mainland AK. By Monday, the ridge axis looks
to be centered right over Southecentral setting the stage for a
decent Memorial Day with mostly dry conditions, clearing skies,
and slightly warmer temperatures than seen over the past week.
Some diurnally driven convection will likely develop over the
higher terrain in the late afternoon hours as warmer temperatures
inland will help develop a thermal trough kicking off showers and
even some possible isolated thunderstorms.

Looking past Memorial Day, models are coming into better agreement
regarding the next system moving in from the Bering, with a front
extending out from a low center over the Eastern Bering moving
across the West Coast by Monday evening into Tuesday morning. The
front does look to weaken some as it moves further east towards
Southcentral during the day on Tuesday as it runs into an upper
ridge axis extending south from the Arctic. The GFS tries to keep
the front more intact as it moves east while the EC rapidly
weakens the system. Regardless, there is consensus in a return to
cooler and wetter weather next week as the upper low builds back
in over the Bering and Western Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...CB
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB
LONG TERM...KVP



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