049
FXAK68 PAFC 140031
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 PM AKDT Mon May 13 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

The surface low that was near Kodiak Island is elongating and
weakening as it heads eastward through the Gulf. Flow across the
mainland Southcentral is shifting from easterly to northerly
offshore with the low passing east. Expect winds to become lighter
as the low continues to weaken and a ridge builds across the
region from the west. With increasing daylight and sunshine
however, sea breezes will become more apparent for coastal areas
with localized onshore flow during the heat of the day.

Scattered showers are moving northeast to southwest across
Southcentral with more towering cumulus development compared to
yesterday with a few lighting strikes noted this evening over the
Western Kenai and in the Susitna and MatSu Valleys. Shower motion
will gradually decrease and shift northerly (and even
northwesterly depending on the position of the Gulf low) late this
evening as flow weakens. Higher areas of convective instability
are located in the Susitna Valley. As the ridge builds across
Southcentral Tuesday and for midweek, weak up Inlet flow will
return.

Southerly flow through the Copper River Basin on Thursday and
perhaps even stronger Friday could aid in further drying through
the Copper River Valley. RHs could dip into the 20 percent range.
Temperatures will be around 60 degrees. Elsewhere, expect sunnier
skies, increasingly drier weather, and warmer temperatures through
Thursday. A front could reach Kodiak Island and the western Gulf
overnight Thursday into Friday morning. At this time, the ridge
over Southcentral appears to be slowed with its progression
eastward, but there is lower confidence in the timing of the
trough.

rux/cc

&&
.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE
ALEUTIANS (Days 1 through 3/ Today through Thursday morning)...

A building ridge will move over Southwest and the eastern Bering,
providing calmer conditions through Tuesday. Simultaneously, a
Kamchatka low extends a warm front across the western Aleutians.
Widespread southerly gale force winds are expected as the system
moves eastward. Warm air behind the front will quickly switch any
wintry precipitation into rain as it passes into the central
Bering Tuesday night. Winds will remain strong across much of the
Bering with gale force winds persisting through Wednesday
morning.

Strong southwesterly flow persists through the morning hours of
Wednesday, when the highest winds, (gale force) are expected
across Nunivak Island and the Kuskokwim Delta. Widespread
precipitation is also expected as the front enters the western
Alaska coastline through Wednesday afternoon.

There are early indications of a new low forming near the Western
Aleutians Thursday morning, but model agreement is low concerning
the strength and location of this feature.


&&
.LONG TERM FORECAST (Days 4 through 7: Thursday night through
Monday)...

The long term forecast for the Southern Alaska will begin with a
ridge over the Gulf of Alaska sliding east as a shortwave trough
rounds the base of a longwave upper-level trough situated over the
Bering and moves over Southwest Alaska. Models quickly diverge
with regard to the evolution of this system, adding plenty of
uncertainty right at the beginning of the long term forecast. All
guidance has the development of a surface low near the AKPen by
Friday as the shortwave deepens. However, both the GEM and EC try
to hold onto the downstream ridging longer, driving the low and
its moisture into Southcentral. The GFS pushes the ridge south and
provides a more progressive solution with the low tracking east
with only scattered showers along the western slopes of the
interior and coastal mountains. This system then exits to the east
late Saturday.

Sunday may offer a reprieve from any extensive cloud cover and/or
shower activity across the Southern Mainland. But, again, all
models are struggling with the track of various shortwaves
embedded within the longwave trough. While guidance shows a ridge
trying to build north from the North Pacific and western Gulf, the
EC and GEM quickly move the ridge axis east over the eastern
Gulf. This solution would place the entirety of the Southern
Mainland on the back side of the ridge with the resultant
southwesterly flow lending to a more unsettled pattern with
various waves moving along the Aleutian Chain and across the AKPen
and Kodiak Island. The result would be more cloud cover and
chances for rain across the region. The GFS is the more amplified
solution, with a more northerly building ridge remaining in place
longer. This result would slow any upstream storm systems and
likely result in a more northerly storm track, keeping conditions
much more tranquil across the Southern Mainland. Given the
consistency of the GFS and a trend of the EC and GEM ensembles
leaning more toward the GFS, the long term is weighted more toward
the stronger ridge solution.

For the Aleutians and Bering, the longwave trough situated over the
region will like keep conditions cool and unsettled through the long
term. Any ridging between storm systems would be brief, with the
best chance for high pressure over the Bering late Friday into
Saturday. Any warmer air associated with the ridge, though, would
likely result in widespread stratus and fog due to the warmer air
riding over the cold open waters.

-TM

&&

.AVIATION...

PANC...VFR conditions will prevail. Expect light winds except
variable and gusty near showers and the very isolated thunderstorm
this evening. Showers and thunderstorms will diminish early this
evening.

-CC


&&


$$