Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
755 PM EDT Fri Mar 25 2022
Valid 12Z Tue Mar 29 2022 - 12Z Sat Apr 02 2022
...Overview...
The primary focus of the forecast will be on a series of
systems/fronts that should bring episodes of enhanced
precipitation and winds from the North Pacific/Aleutians/Bering
Sea into the Gulf of Alaska and nearby land areas. There is
decent agreement on the general pattern but more spread on
important details that will affect the location and magnitude of
greatest precipitation and winds. Expected flow aloft over the
mainland appears somewhat ambiguous for at least portions of the
period. Best consensus of guidance highlights a mean ridge to the
north/northwest of the mainland, a trough/upper low to the east,
and a mean ridge over western Canada (briefly dampened by a
shortwave or two). This may leave a col region over the mainland
for a time but by later in the week a moderate majority of
guidance suggests a tendency for the western Canada and Arctic
ridges to connect to some degree.
...Guidance/Predictability Assessment...
In principle there is decent clustering for the leading system
heading toward the southeastern coast/Panhandle Tuesday into
Wednesday. Small-scale aspects of the system still temper
predictability for specifics though. Most solutions currently
show a frontal wave tracking northward close to the Panhandle
while the parent low south of Kodiak Island early Tuesday could
track eastward behind it.
Additional complexities exist with the upstream area of low
pressure progressing eastward from the Bering Sea/Aleutians. At
the very least the prevailing theme in latest guidance is that the
core of upper dynamics should not extend as far
eastward/southeastward as depicted in recent GFS runs, so the
greater probability is for the parent low to track over the Bering
Sea rather than over or south of the Aleutians. The GEFS mean is
somewhat south of the ECMWF/CMC means but not to the degree of the
GFS. Details of energy aloft will also determine how frontal
waviness may evolve after midweek. ECMWF runs have been
suggesting such a wave that may track into the far southwestern
mainland, even with an upper evolution closer to consensus than
the GFS (which ultimately keeps the wave farther south). On the
other hand the 12Z CMC is much more progressive, pushing a frontal
wave more toward the Panhandle. The scale of this frontal
waviness is too small to be reflected in the ensemble means.
Finally, there is a hint of another progressive low/front that
could arrive from the west with upstream energy feeding into the
eastern Bering into Pacific mean trough aloft.
Models and ensembles show yet another storm tracking into the
Aleutians/Bering Sea by day 8 Saturday. Some operational runs
suggest it could be fairly deep. Latest ECMWF runs stray to the
east or southeast side of the full guidance spread and a slower
trend in the new 12Z ECMWF mean would further suggest that the
operational ECMWF scenario has relatively lower probability so far.
Recent GFS/ECMWF runs have differed considerably for specifics of
upper flow over the mainland during the period, with the GFS
tending to favor more troughing that extends from the northeast
(though less pronounced in the 12Z/18Z runs) versus the ECMWF that
wants to extend ridging northwest from western Canada. The full
model/ensemble consensus suggests there may be a col region over
the mainland into midweek, followed by the ensemble means being
fairly consistent in developing more of a ridge per ECMWF runs.
Guidance comparisons led to starting the first half of the
forecast with a 12Z operational model blend with slightly less GFS
input than average due to its lower-confidence evolution over the
Bering Sea/North Pacific during that time frame. Phasing in some
of the 12Z GEFS/00Z ECMWF means to complement the operational runs
after early Thursday reflected the most agreeable aspects of
significant features.
...Weather/Hazard Highlights...
The leading system reaching the Gulf of Alaska should promote a
period of moderate to heavy precipitation over the southeastern
coast/Panhandle through Tuesday. The next low/frontal system over
the Bering Sea and Aleutians will initially be accompanied by some
organized precipitation and enhanced winds. By mid-late week a
wave may develop along the front just south of or near the Alaska
Peninsula--helping to focus precipitation over
southward/eastward-facing locations along the Peninsula and
farther east. Confidence is not yet great in the details though,
as a more progressive minority scenario would push greater precip
focus into the Panhandle instead. Another system merging into the
larger scale circulation could maintain some degree of moist flow
into parts of the southern coast through the end of the week. A
potentially strong storm may bring another episode of
precipitation/winds to the Bering Sea and Aleutians by next
Saturday.
Most of the southwestern half of the mainland will likely trend
toward above normal temperatures with the highest anomalies over
far southwestern locations. The remainder of the mainland should
see a mix of above/below normal readings. Best potential for
below normal temperatures should be over the North Slope and for
morning lows. Expect the Panhandle to see below normal highs and
near to above normal lows.
Rausch
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Tue, Mar 28-Mar 29.
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