Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 031211

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
411 AM AKDT Wed Jun 3 2020


The upper level pattern remains amplified as upper troughing
currently extends across the Gulf of Alaska while upper ridging is
building into the western Bering/Aleutians. A vertically stacked
low at 55N 153W is slowly moving northeastward. This low is
currently weakening due to the combination of being vertically
stacked as well as being far away from the subtropical-jet, thus
the synoptic scale forcing is weakening. The subtropical-jet
currently remains south of 50N across the North Pacific and
extends northeastward from Midway Island to southern British

At the surface, radar imagery shows showers moving south-
southwestward across the Kuskokwim Delta into northern Bristol
Bay. Radar also shows light shower activity moving northwestward
across the northern Gulf into Prince William Sound and the
southern Kenai Peninsula.



Guidance is in good agreement with the placement and intensity of
synoptic scale features through day 3. Models show the vertically
stacked low gradually weakening as this low will continue to lose
synoptic scale support as the subtropical-jet shifts
southeastward. Models also have a more consistent forecast with
respect to mesoscale features as both the GFS and NAM show similar
solutions with the timing and intensity of upper level waves
moving across the Alaskan mainland. There is also consistency with
respect to the stability indices for this afternoon and this will
lead to a higher confidence in the convective forecast.


PANC...VFR conditions will persist for this TAF package. Gusty
southeasterly Turnagain winds will gradually subside through 18z.
There is high confidence that these gusty southeasterly Turnagain
winds will continue after 00z, then ease after 15z on Thursday.



The stacked low complex south of Kodiak Island continues to move
east and weaken. Broad easterly winds across the Gulf will keep
chances of stratiform rain over Kodiak today and along the
southern and eastern Kenai Peninsula. Weak upper waves propagating
west-southwest across the mainland will continue the threat of
showers across Southcentral through tonight. A weak coastal ridge
and lower pressure inland will give rise to gusty easterly winds
across Turnagain Arm today and allow the winds to bend into south
and west Anchorage this afternoon and evening. There also may be a
gusty southeast wind out of the Knik River Valley this afternoon.

On Thursday, upper short waves dropping south across Southcentral
combined with low level warming will kick off showers across
Southcentral. Stability indices support chances of isolated
thunderstorms across the Copper River Basin and Talkeetna
Mountains during the afternoon and evening. Expect gusty southerly
winds and locally stiff sea breezes along Cook Inlet and over
Kachemak Bay and Resurrection Bay in the afternoon.


The thermal trough that has been over southwest Alaska will shift
north today as somewhat cooler air moves in. It will be a much
more stable air mass, allowing the precipitation chances away from
the mountains to greatly diminish, and thunderstorms are not
expected at all today. A front moving in from the west on Thursday
afternoon and evening may kick off a thunderstorm or two as the
atmosphere becomes slightly more unstable, but this risk looks
small at this time.


A rather quiet period is expected across the Bering and Aleutians
for the next couple of days. High pressure will be over the
southern Bering and Aleutians, with low pressure to the north.
This low pressure will drift southward on Thursday, allowing some
precipitation to move into the west central Bering.

.MARINE (Days 3-5: Friday through Sunday)...
Model guidance continues to show quiet weather expected throughout
the forecast period Friday through Sunday for all marine areas
with light winds and low waves. Westerly flow will continue across
much of the Bering throughout the forecast period. A weak low
pressure system is expected to drift southeastward through the
northern Bering Friday afternoon and evening while continuing into
the east-central Bering through Sunday afternoon which will shift
winds to more northwesterly Sunday afternoon.


.LONG TERM FORECAST (Days 4-7: Saturday through Wednesday)...
Model guidance is in the best agreement for the first two days of
the forecast period (Saturday and Sunday) with the placement of an
upper low over the eastern Bering/Southwest Alaska. The exact
placement of this low remains in disagreement however, which will
have an impact on the sensible weather during the period. Beyond
Sunday, model spread becomes even greater with the ECMWF bringing
the upper low south into the North Pacific whereas the GFS keeps
it further north over Southwest Alaska. This will have major
implications on the sensible weather across Southwest Alaska and
Southcentral with possible large fluctuations to the ongoing
forecast possible from day to day. Due to the differences in the
model guidance, the forecast long term is about average for
Saturday and Sunday with low confidence for Monday through
Wednesday. With these differences in the model guidance, it makes
even depicting if temperatures will be above or below normal hard
to tell at this point.





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