Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
753 PM EDT Sun Mar 27 2022
Valid 12Z Thu Mar 31 2022 - 12Z Mon Apr 04 2022
...Overview...
Today's models and ensembles still show an active pattern over the
North Pacific and vicinity, bringing periods of enhanced
precipitation and/or brisk to strong winds across the Aleutians
and southern coast of the mainland. Highest precipitation totals
should be along the Alaska Peninsula into the Kenai Peninsula with
some moisture extending to the Panhandle as well. Guidance shows
elongated ridging aloft over the mainland late this week but
energy within cyclonic flow to the east/northeast may lower
heights thereafter as a high closes off over the Arctic. At the
surface, the mainland will likely be in a persistent gradient
between Arctic high pressure and North Pacific/Bering Sea lows.
...Guidance/Predictability Assessment...
A 12Z GFS/ECMWF/CMC blend early followed by inclusion of the 12Z
GEFS/00Z ECMWF means along with those models later in the period
provided the best account for the most common themes of
guidance/latest refinements and then resolving differing ideas for
specifics within a fairly agreeable large scale pattern.
Over the past day guidance has trended stronger with a developing
frontal wave that should track to around the Alaska Peninsula by
early Friday. Latest ECMWF/CMC runs have gravitated somewhat
toward GFS runs that have tended to keep the system near the
Peninsula versus continuing into the Bering Sea or southwestern
mainland. As has been the case in recent days, there is still a
minority scenario that is farther east--now represented by the 12Z
UKMET and CMC mean instead of the CMC that had previously served
that role. The stronger depiction of this wave has led to a
moderate westward adjustment for heaviest associated
precipitation. Continuity is good for rapidly arriving upstream
energy to interact with the upper dynamics to yield low pressure
near or south of the Alaska Peninsula by early Saturday, though it
remains to be seen whether by persistence of the original low or
redevelopment.
There are still notable differences for developing western Pacific
low pressure that should track across the Aleutians/southern
Bering Sea during the weekend, with emphasis transitioning to or
near the Gulf of Alaska by next Monday. Operational model
differences include the latest GFS/CMC runs tracking the parent
low into the Bering Sea with a leading frontal wave ultimately
reaching the vicinity of the Gulf in contrast to the ECMWF that is
faster and farther south with the main low, with the system itself
tracking into the Gulf. UKMET runs have been on the fast side of
the spread thus far. The ensemble means have been favoring a
primary system track into the Bering Sea though perhaps not
holding it as far west as some CMC runs, while hinting at
potential for leading triple point development. The preferred
model/mean blend offers reasonable continuity and a good
intermediate evolution relative to the array of guidance.
Over the past day or so the guidance has shown a tendency for
mainland ridging aloft as of Thursday to be replaced by a weakness
as a high closes off over the Arctic and energy arrives from
cyclonic flow to the east/northeast of the mainland. Confidence
in specifics is not great given the complexity of the flow.
...Weather/Hazard Highlights...
A fairly vigorous developing North Pacific frontal wave tracking
toward the Alaska Peninsula Thursday should bring an episode of
locally heavy precipitation and brisk to strong winds to the
Peninsula and vicinity. Highest totals should be along the
eastern half of the Peninsula and perhaps as far east as the Kenai
Peninsula. Specifics will depend on small-scale system details
that tend to have low predictability a few days out in time.
Moisture along this system's leading front as well as a trailing
front will likely bring a couple periods of precipitation into the
southeastern coast and Panhandle. A strong upstream Pacific
system should track into the Bering Sea or Aleutians, with either
the system itself or a leading wave reaching into or near the Gulf
of Alaska by early next week. Details of this evolution remain
unresolved but most possible scenarios would bring a period of
precipitation and brisk to strong winds to the Aleutians, followed
by precipitation of varying intensity reaching the Alaska
Peninsula and southern coast/Panhandle.
Continue to expect mostly above normal temperatures over the
southwestern half of the mainland, with greatest anomalies for
highs over far western areas and those for lows somewhat more
widespread over the south and west. The rest of the mainland
should see a mix of above/below normal readings, with below normal
temperatures most likely over the North Slope/northeast-interior
part of the mainland. The transition of the upper pattern from
moderate ridging on Thursday to some degree of troughing or shear
axis may lead to a gradual cooling trend over some areas during
the period. The Panhandle will likely see below normal highs and
near to above normal lows.
Rausch
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