FXAK68 PAFC 021236
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
436 AM AKDT Thu Jul 2 2020
.ANALYSIS AND UPPER LEVELS...
On the planetary scale, the Rossby Wave pattern continues to
increase in amplification. The upper trough is located over the
Bering/Aleutians and the upper ridge extends northward from the
subtropical North Pacific into western mainland Alaska.
Teleconnections support the upper ridge continuing to build across
mainland Alaska while the upper trough is expected to remain over
On the synoptic scale, the subtropical-jet extends northeastward
from southern Japan to the western Bering/Aleutians. The jetstream
then sharply cuts south-southeastward into the subtropical
central Pacific (near Midway Island), then sharply cuts north-
northeastward to over Bristol Bay and the Seward Peninsula. An
upper low continues to remain nearly stationary over eastern
Siberia. A second upper-low over northeastern Alaska is slowly
On the mesoscale, showers are moving southeastward across the
northern Gulf of Alaska from the Kenai Peninsula and across
Guidance is in good agreement over the next 72-84hrs with the
placement and intensity of synoptic scale features at both the
surface and in the upper levels. Due to this agreement, forecast
confidence is high. High resolution models were favored to resolve
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
The general pattern across Southcentral the next couple of days
will be dominated by an upper level ridge. This will promote a
continued warming and drying trend through the holiday weekend.At
times, weak shortwaves or upper level disturbances will move
through the flow. As a result, the risk exists for an isolated wet
thunderstorm or two mainly across the Alaska, Talkeetna and
Wrangells beginning Friday afternoon and continuing again for
Saturday afternoon. The air is expected to remain a bit more
stable across the Chugach Mountain Range, therefore, the
thunderstorms were left out of the forecast at this time.
Instability is very marginal but enough to have introduced the
risk for an isolated wet thunderstorm with the threat for a
lightning strike. Most of the activity will be of the heavy
downpour variety but the risk is there for one cell to become
Also, since temperatures warmed higher than projected across parts
of Anchorage, for example, Campbell Creek reached 75 degrees
yesterday, temperatures were raised slightly across the Anchorage
Bowl and the Mat-SU valleys for today and the next few days. Low
temperatures were lowered some across inland areas especially
Campbell Creek in the Anchorage Bowl and across the Copper River
Basin. Based on the latest model guidance, any showers and storms
that do develop should remain confined to the mountains as the
flow looks weak enough to not move this activity off the mountains
especially today and tomorrow. This is a high-bust potential
forecast for temperatures as if more clouds are present than
currently forecasted, temperatures could end up a few degrees
cooler than projected.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Thursday
Frontal rainfall associated with a low in eastern Siberia can be
seen in radar this morning extending from Aniak to Dillingham.
This front will continue to push eastward throughout the day
today, but precipitation is expected to slowly dissipate by the
time the front reaches the Alaska Range Friday night. With the
passage of the front, upper level flow over Southwest Alaska will
transition from southwesterly to westerly, which will help to
advect a maritime layer over the region and bring low stratus and
patchy fog to coastal areas tonight and Friday night. Overcast
conditions will also help to keep high temperatures in the 50s and
60s over coastal areas, with inland temperatures in the mid to
upper 60s through Friday. As the ridge builds back overhead on
Saturday, temperatures will likely climb into the 70s over the
inland areas of Southwest. Showery activity is expected over the
Akpen through Saturday as some weak upper level energy moves
overhead from the north Pacific.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Thursday through Saturday)...
An upper level low over the western Bering will continue to move
northeast towards the Norton Sound today. Its corresponding
surface low will continue to weaken as the system moves, with
small craft winds diminishing along the front near the Yukon Delta
by midday today. As the system pushes out, a high amplitude ridge
will build over western Alaska through Saturday, which will allow
for lighter winds and low stratus over the eastern Bering through
The next upper level wave is expected to move off of the Kamchatka
Peninsula early Friday morning. This system has some decent
baroclinicity for this time of year, with a 850 mb temperature
spread of 10 degrees celcius across the warm and cold sectors of
the system. Due to the ridging over western Alaska, the upper
level energy stays nearly stationary over the Western Bering. As a
result, the main weather features will be two rounds of frontal
precipitation and small craft winds over the western
Bering/Aleutians. The first front will impact the western Bering
on Friday, with the second front moving from the western Bering
Friday night and reaching Dutch Harbor by Saturday night.
.MARINE (Days 3 through 5: Saturday through Monday)...
Gulf of Alaska: Easterly winds along the North Gulf Coast yield
to Westerly winds spreading across the Gulf by Mon. Confidence is
good the winds remain below small craft levels.
Aleutians and Bering: A elongated Western Bering low slips
towards Northern Kamchatka. Confidence is good for widespread
small craft winds and waves spreading from the Aleutians into the
Bering through Mon with pockets of Gale winds and waves across the
Central Aleutians dissipating through Sun.
LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...
The strong upper ridge over western Alaska Sunday weakens through
Wednesday. This allows short waves spinning off of the Bering Sea
trough to progress eastward across the Mainland. This pattern
change will bring intrusions of moisture from the west resulting
in cloudier conditions, increased chances of rain/showers, and a
lowering of daytime high temperatures across the southern
Mainland. Although the model trends are similar with the weakening
of the upper ridge, differences in solutions will pose a problem
in timing systems. So confidence is low on exact timing but fair
to good on a trend toward more clouds, cooler temperatures, and
chances of rain.
With the main upper low center and trough holding over the Bering
Sea expect generally mostly cloudy conditions with periods of
rain/showers, and gusty winds.
SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ