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000
FXAK68 PAFC 160130
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
530 PM AKDT Sat May 15 2021

.ANALYSIS AND UPPER LEVELS...
There is a low over the Eastern Aleutians as well as just south of
Prince William Sound this afternoon. The Eastern Aleutian low is
the stronger of the two as there is still a little bit of upper
level support feeding into it. This is a mature low that is
wrapped up a bit with shower activity around all sides of it.
The low near Prince William Sound is bringing some showers to
the Kenai Peninsula and more persistent rainfall to the north
Gulf coast. This is a pattern change from the past few days in
Southcentral so the winds are also lower across the region,
especially those through channeled terrain.

The greatest amount of convective instability in Southern Alaska
this afternoon and evening is right along the Alaska Range in the
Copper River Basin and far northern Susitna Valley.

&&

.MODEL DISCUSSION...
Model guidance remains in good overall synoptic agreement the next
few days. The challenge will be with the timing and strength of
any weak upper level waves that develop in Southcentral.
Southwest Alaska will have the upper level ridge start to
influence it, but there remains cool temperatures aloft so any
shortwave could cause some showers. This is something to watch on
some of the upcoming model runs.

&&

.AVIATION...
PANC...On and off showers will persist through the day and bring
ceilings just below 5,000` at times. The Turnagain Arm wind will
return again this evening, though the timing could vary by an hour
or two. Confidence is high that it will be weaker than it was on
Friday. The winds will dissipate overnight as ceilings start to
lift.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 2: Tonight
through Monday)...

A weakening upper trough axis sprawled out along the North Gulf
Coast has spread areas of cloud cover into the most of the
southern portions of Southcentral this afternoon. A weak surface
low is bringing bands of rain into the Prince William Sound area,
with more showery activity ongoing over the western Kenai
Peninsula and near the Matanuska Valley area. Most of these
showers should gradually die off through tonight, and steadier
rain likewise will let up near the PWS as the low moves inland and
dissipates by tomorrow afternoon.

Farther north, breaks in the cloud cover over the Copper River
Basin and Susitna Valley have allowed temperatures to warm to near
60 F in valley locations. Similar to yesterday, surface heating is
generating some low level convective instability here, especially
close the the northern Alaska Range. In addition to widely
scattered showers, a stray thundershower or two is possible for
the far northern Susitna Valley and along the northern Alaska
Range through this evening until around sunset.

From late Sunday into Monday, a weak upper ridge will build in
from the southwest while an upper level low tracks over the Gulf.
This will bring increasingly offshore flow and clearing skies for
much of Southcentral by Monday, with drier and warmer conditions
returning for all but the Copper River Basin where there will
again be the potential for afternoon showers moving off of the
mountains near and after peak heating of the day.

&&

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

The remnants of an upper low continue to churn over the Central
and Eastern Bering. This system has ejected minor shortwaves into
portions of SW Alaska resulting in showers which have been
detected by the radars at Bethel and King Salmon. This upper low is
going to continue to weaken and push southeastward. A weak upper
ridge will move into SW Alaska late Sunday resulting in a warming
and drying trend. The models continue to advertise a compact upper
level low over NE Russia and this system will clip the Y-K Delta
on Tuesday. Otherwise, most of SW Alaska will experience a warming
trend.

&&

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

An upper level low centered over Nikolski today continues to
eject shortwaves. The upper low will continue to weaken and move
southeastward today and tomorrow. The Central and Eastern
Aleutians as well as the AKPEN will continue to see light rain
showers today, tonight and early tomorrow as the low track
southeastward. A dome of high pressure enters the western Bering
Sunday morning bringing a lull in activity. A pair of lows will
move south of the chain Tuesday increasing the potential for rain
along the chain, especially the Central Aleutians. The run to run
continuity with the models has been poor as of late with storms
moving into the Bering and in the NW Pacific. There could be some
changes for precipitation for the Aleutians for Tuesday.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

High pressure with generally light winds across most of the
Bering through Thursday. A North Pacific low tracks just South of
the Aleutians for Thursday. Models in good agreement. The wind
wrapped North Pacific low brings small craft winds over the
Central Aleutians and Alaska Peninsula Wednesday, increasing to
gale force winds spreading into the Southern Bering Thursday. High
pressure moves across the Gulf. Gusty gap winds around Kodiak
Island Tuesday and Wednesday. Small craft winds with the
approaching low become gale force winds over the Western Gulf and
Kodiak Island Thursday. Seas to 12 feet south of Kodiak Island.

&&

.LONG TERM FORECAST (Days 3 through 7...Tue through Sat)...
Conditions will remain relatively quiet across the area for most
of this time period. The early part of the week will feature
weak flow over much of the mainland allowing for convection
along the mountains. Temperatures will continue to hold very close
to normal for mid-May. By next weekend, there are some signs of a
much more summer-like pattern building over the state from the
east. Here are the details:

Tuesday and Wednesday, there will not be any dominant weather
feature across southern AK or the Aleutians. This will create
partly cloudy conditions for the mainland with afternoon showers
possible each day. As temperatures slowly warm in response to
increasing daylight/climatology, we could start to see some more
thunderstorm activity as we move towards the middle of the week.
Any chance for this will be centered along the thermal trough and
near the mountains. High temperatures will continue to hover in
the mid 50s to low 60s for locations further inland.

By Thursday and Friday, a system dropping across the northwest
Bering Sea will phase with some energy over the North Pacific. The
interaction will be somewhere near the Central Aleutians and
result in a developing surface low. This system will bring a
return to wind and rain to the Eastern Aleutians and Alaska
Peninsula as it moves to the east. By Fri, this system will start
to bring rain back into Southwest AK and Kodiak Island. For
Southcentral, this low will struggle to make much progress inland
as a ridge of high pressure starts to build near the ALCAN border.
While there is still a moderate to high amount of uncertainty
this far out, there are indications that this ridge could start to
bring some of our warmest temperatures of the year thus far (850
mb/5000` at 10-15C). Generally this forecast leans on the EC and
GFS ensemble means to handle the uncertainty.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...KZ/MO