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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 2359Z Feb 27, 2024)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
659 PM EST Tue Feb 27 2024

Valid 12Z Sat Mar 02 2024 - 12Z Wed Mar 06 2024

...Very cold temperatures over a majority of the state late this
week into the weekend...


...Overview...

Model guidance indicates an amplified upper pattern across Alaska
through the end of the week, consisting of a narrow ridge atop the
Alaska Peninsula through the eastern Bering Sea and the western
Mainland on Saturday with troughing on either side. Northerly mean
flow, lingering troughing in the eastern Interior, and cold
surface high pressure will promote very cold temperatures over
much of the state late week. Into early next week, the fate of the
ridge becomes the main question that has shown ample spread in the
models. There seems to be a tentative consensus building that
ridging will persist rather than be quickly eroded by energies
coming in from the northeast and west. This provides more quickly
moderating temperatures especially to western and central parts of
the state while reducing precipitation chances for Southeast
Alaska early next week.


...Guidance Evaluation and Preferences...

Model guidance is in good agreement for the start of the model
diagnostics period Saturday in showing troughing across the
Aleutians pushing a frontal system eastward toward the Alaska
Peninsula, while narrow upper ridging is in place to the east with
another trough poking in from northwestern Canada downstream of
that. Cold surface high pressure is also agreeable. But by
Sunday-Monday, models have struggled tremendously to reach a
consensus even on the synoptic scale. After a trend with 12Z
models on 2/26 to indicate more upper troughing across the
Interior as energy especially emerging from the northeast eroded
the ridge, today's models are trending toward more ridging
remaining into early next week, though not uniformly. The main
holdout into the 12Z cycle that still showed troughing into Day
6/Monday was the 12Z GEFS mean, as the 12Z GFS and CMC did switch
to a ridge pattern after earlier runs indicated a trough. ECMWF
runs from 12Z and 00Z showed ridging and so did the 00Z ECMWF mean
that was available at forecast production time (after the 12Z EC
mean from 2/26 was troughy). So with the bulk of guidance now
showing a ridge persisting, today's forecast leaned in this
direction. The incoming 18Z GEFS mean has started to trend toward
more of a ridge through Monday as well, which may be a good sign,
though it is not as strong as other models/means.

By Tuesday, the ridge does seem to start getting shunted east and
eroding as stronger Bering Sea troughing comes in from the west. A
brief bout of ridging may be possible over the Aleutians/Alaska
Peninsula Tuesday-Wednesday while additional energy emerges from
the Bering. Surface lows and frontal systems are likely for the
Bering/Aleutians but certainly the details will evolve with time.

Given these considerations, the WPC forecast used a model blend
favoring the 12Z ECMWF/CMC/GFS and 00Z EC mean, leading to upper
ridging remaining more amplified across the state through early
next week. Increased the proportion of the EC mean to about half
by the end of the period.


...Weather/Hazards Highlights...

As highlighted on the Days 3-7 Hazards Chart, the pattern late
this week will support a broad area of hazardous cold temperatures
across a majority of the mainland to the south of the Brooks
Range. This will be from a combination of actual air temperatures
(possibly approaching -40 degrees over the typically coldest
eastern Interior locations) or wind chills farther south and west.
Much below normal temperatures are also likely for Southeast
Alaska. Temperatures should gradually moderate from west to east
through the weekend into early-mid next week, especially
considering the trend toward a sustained upper ridge. Northwestern
areas of the state look to reach above normal temperatures this
weekend and last into early-mid next week.

A Bering Sea frontal system and trailing wave will spread
organized precipitation across the Aleutians/Bering Sea and
into/near the Alaska Peninsula into Saturday. Some moisture could
stream farther north and affect western parts of the state with
mostly light snow. Persistent mean southwesterly flow should
promote precipitation chances remaining across the Alaska
Peninsula, Kodiak Island, and the southwestern Mainland into early
next week. Some light snows may impact much of the Interior by
around Tuesday. Meanwhile, the trend toward a stronger ridge
across the Interior also leads to significantly lowered
precipitation chances for Southeast Alaska given the dry mean
northerly flow. So if this forecast holds, only light
precipitation is likely there with perhaps a wetter shift into
midweek. Winds and precipitation may be enhanced for the Aleutians
again next week when frontal systems pass through. There could
also be concerns for localized gap/outflow winds farther east
across the southern coast of the state, but there is not any good
consensus for strong winds at this point.


Tate


Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html