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FXAK68 PAFC 240106
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 PM AKDT Wed May 23 2018

.ANALYSIS AND UPPER LEVELS...

The same weather pattern that has been experienced over the past
couple days in Southern Alaska continues today as a weak upper
level low sits over the Gulf pushing showers across the north Gulf
coast and the southern mainland. Southcentral is seeing more
cloud cover today due to the weak ridging that has moved
northward.

The main weather driver this afternoon is the front over the AK
Pen associated with a southern Bering low moving east across the
central Aleutians. This front is bringing steady precipitation,
low ceilings, and gusty southeasterly flow to southwest Alaska. A
weak triple point low is developing south of the AK Pen, which
will help lift the front into the Gulf.

&&

.MODEL DISCUSSION...

Models are still having difficulties in the position of the triple
point low as it moves into the Gulf on Thursday, which will impact
the strength of the barrier jet along the north Gulf coast. The
NAM and EC seem to be in closer position agreement with a
stronger barrier jet, so these models are favored over the others.

The models are in good agreement with the low in the southern
Bering as it crosses south of the Aleutians through Friday.
However, models are struggling to place the center of this low as
it makes its way into the Gulf on Saturday, but will have little
to no impact on the forecast in the area.

&&

.AVIATION...
PANC...VFR conditions are expected to persist through the TAF
period. Gusty southeast winds out of Turnagain Arm should move
back into the terminal early this evening in response to surface
heating in the southern Susitna Valley. These winds have been
delayed due to more extensive cloud cover in the Susitna Valley
keeping temperatures a little lower and the western Kenai
Peninsula heating up more which is delaying the Turnagain Arm
winds moving over the airport, but they still will likely move in
early evening and then subside some after 12z but are expected to
remain out of the southeast through Thursday morning. Winds will
then increase again by Thursday afternoon as a front approaches
the north Gulf Coast.

&&

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

The current trough situated east of Kodiak Island will continue
to lift northward tonight aided by an advancing warm occlusion
over the Aleutians. A new triple point low will develop southeast
of Kodiak Island and lift into the southern Gulf Thursday. Coastal
locations will remain rather wet through Friday as a widespread
southeasterly flow persists. For the interior, scattered showers
will develop Thursday afternoon and evening as a sheared vorticity
maximum advects west to east from the Copper River Basin toward
the Susitna Valley. Although a greater potential for convective
development is hinted at in the forecast models for Thursday,
there is still a low probability for thunderstorm development at
this time. On Friday, a transient upper-level ridge will slide
across the interior. This should help inhibit convective
development and confine any shower activity to the higher terrain.

With little pattern change, expect the gusty diurnal gap winds to
continue for Turnagain Arm, south and west Anchorage, Palmer, and
the Copper River Basin through Friday evening. The strongest gusts
are expected Thursday evening as a building coastal ridge tightens
the pressure gradient across Southcentral Alaska in response to
the developing surface low tracking north into the Gulf.

&&

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

Scattered showers develop through Thursday along an easterly
propagating wave. Isolated thunderstorms are possible across the
Kuskokwim Valley this evening as the thermal trough across the
Central Interior extends toward Sleetmute. Gusty southeasterly
winds taper down later tonight as the front along the Southwest
coast diminishes, with the driving surface low filling on its
track toward the Alaska Peninsula. Patchy fog is possible each
morning morning as winds go light where the air mass is briefly
stable. The interior thermal trough shifts each day bringing focus
for isolated thunderstorms to the Kuskokwim Delta on Thursday and
Friday evening with storms also possible for the Kuskokwim Valley
on Friday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

The Bering low tracks slowly across the Alaska Peninsula on Friday
with a ridge building across the western waters in its wake. This
pattern brings less active weather for much of the Bering, however
the eastern Bering stays in a showery regime on Friday as a
shortwave dives south from the Bering Strait. The ridge only
brings a brief weather pause with the next North Pacific front
racing across the western Aleutians and Bering on Saturday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Starting Saturday, an upper level low will move over the southern
portion of the Gulf of Alaska while a ridge builds over the
western half of the Bering Sea and into SW Alaska. A front
extending out ahead of the associated surface low in the Gulf will
spread rain and wind over the Panhandle while leaving most of
southcentral dry as a weak upper ridge axis tries to build over
over the central and western portions of the state. This should
set the stage for a decent Memorial Day weekend over most of
southcentral and SW Alaska with a few breaks in the cloud cover
and mostly dry conditions, though diurnally driven rain showers
will likely develop over the higher terrain in the late afternoon
hours. Right now, Memorial Day looks to the nicest day of the
weekend over most of the southern mainland as the upper ridge axis
moves over southcentral allowing clouds to scatter out a bit
more, though temperatures look to be right around average for this
time of year.

Models show some disagreement regarding how long this period of
somewhat nicer weather will last, with the EC being the more
progressive solution moving the next front into the SW mainland by
Monday afternoon, while the GFS brings the front across a bit
later on Tuesday. Either way, models are consistent in
redeveloping the upper low over the Bering by early to mid next
week bringing a continuation of the cooler and wetter pattern that
has been plaguing the region since mid April.

&&

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

&&
$$

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