Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
704 PM EDT Tue Mar 15 2022
Valid 12Z Sat Mar 19 2022 - 12Z Wed Mar 23 2022
...Overview...
The most notable feature over Alaska for the medium range period
will be an upper low with possibly multiple centroids at times
meandering in the Gulf of Alaska. Initial energy near the Alaska
Peninsula combined with an active storm track across the
northeastern Pacific will serve to redevelop and reinforce mean
low pressure across the Gulf through early next week. A series of
low pressure systems will bring a sustained period of unsettled
weather through the Panhandle and occasionally up into the
southern coast for much of the period. By late period, another low
near the Kamchatka Peninsula will swing a cold front through the
Aleutians, but a blocky upper ridge setting up near/over Mainland
Alaska will probably keep the low from much eastward progression.
...Guidance/Predictability Assessment...
On the large scale, the models show fairly good agreement with the
pattern, but still present quite a bit of uncertainty at the
surface regarding details of low pressure systems in the Gulf and
how said systems interact with each other. This shows plenty of
differences in strength and position of the lows, which has
implications for hazards along coastal regions. Given the small
scale nature of these details, it will likely take at least a
couple of days to resolve these. Felt it best to use a general
model compromise between the 12z runs of the GFS, ECMWF, CMC, and
UKMET which seemed to offer a good middle ground and compromise
between the possible solutions.
By early next week, troughing should begin to amplify more over
the Mainland, with a compact embedded low in the Gulf. Prior runs
of the ECMWF took this low by mid next week farther east into
western North America than the GFS or CMC, but the 12z run today
adjusted back westward more in line and usable. Upper ridging
building over the Bering Sea will keep another low near the
Kamchatka Peninsula from much progression eastward, though the
ECMWF is a little bit more aggressive/farther east with the cold
front through the Bering/Aleutians which pushes the blocky upper
high more into the northern Mainland. The greatest outlier
solution is the 12z GFS which breaks off a deep surface low from
the main low, sending it south of the Aleutians by days 7-8. This
is unsupported by any of the other deterministic solutions. For
days 7 and 8, the WPC blend trended towards the ensemble means,
with smaller contributions from the ECMWF and CMC for added system
definition.
...Weather/Hazard Highlights...
Precipitation through the period is expected to focus along
southern parts of Alaska given the northern Pacific storm track.
South-central Alaska to the Panhandle in particular should see
rounds of enhanced precipitation, with varying intensity depending
on location of the surface lows and the orientation of the upper
trough/low. While precipitation does not appear to be very
intense, recent heavy rain/snow across the area could make it more
sensitive to additional impacts, and amounts may pick up by early
next week. In addition, brisk winds are expected with the approach
of a surface low into Saturday with some gusty winds possible
across the Panhandle. On the other side of the lows, periods of
breezy northerly winds are expected over the Aleutians, along with
some chances of snow showers. Snow is also possible for the
eastern mainland over the weekend.
With plenty of troughing aloft, colder than average temperatures
are forecast across the majority of Alaska through the period. The
greatest anomalies (10-20 below average) are expected initially
across western/southwest Alaska, with a gradual eastward
progression into central Alaska this weekend and early next week.
Across the North Slope and southeast Alaska, temperatures should
average closer to normal. Morning lows, however, may actually be
above normal for these same regions through the period, with
interior Alaska min temperatures closer to normal.
Santorelli
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