Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
701 PM EST Fri Jan 24 2025
Valid 12Z Tue Jan 28 2025 - 12Z Sat Feb 01 2025
...Colder trend to well below normal temperatures next week with
enhanced gap winds possible next Thursday...
...Overview with Guidance Evaluation and Preferences...
As the medium-range period begins next Tuesday, guidance continues
to show better agreement on the departure of a significant low
pressure system off to the east and northeast of mainland Alaska,
followed by an abrupt change to a cold regime for the remainder
of next week. A trailing piece of 500mb trough in the wake of the
departing low is forecast to dig southeast across the Alaska
Peninsula by next Tuesday into Wednesday. Deterministic solutions
as well as ensemble means show reasonably good agreement on this
feature till Tuesday before they begin to diverge on Wednesday in
terms of how much this trough will further amplify downstream over
the Gulf of Alaska for the latter half of next week. The 12Z
Canadian model (CMC) appears overly aggressive in this regard as
it spins up a cyclone that is much deeper and much farther west
than its ensemble mean just off the Alaska Peninsula. This
solution is not supported by both the GFS and ECMWF as well as
their ensemble means.
Despite the divergence of the deterministic solutions noted above,
ensemble means from the GEFS, ECMWF, and CMC are converging toward
a gradually weakening cyclone centered over/near the Gulf of
Alaska for the latter part of next week. Guidance in general is
showing a period of enhanced precipitation heading onshore in the
vicinity of the Panhandle midweek with some spread on the
north-south extent of the heavy precipitation. The enhanced
precipitation is generally forecast to slide southward down the
Panhandle through late next week. Meanwhile, guidance is showing
good agreement for an arctic high pressure system to build east
into the northern half of Alaska.
Over the Aleutians, guidance is indicating general agreement for a
large-scale cyclone to edge into the island chain from the west
from midweek onward, with significant divergence of the
deterministic solutions on Days 7 and 8. Ensemble means are in
relatively good agreement though.
The WPC medium-range forecasts were derived based on a consensus
of the 12Z ECMWF and 00Z/12Z EC mean, the 12Z GFS/GEFS, and the
CMC mean. The CMC deterministic solutions were kept only for the
beginning of the forecast period. This blend yielded a solution
very compatible with WPC continuity.
...Weather/Hazards Highlights...
As the cyclone departs mainland Alaska next Tuesday, the remaining
snow across interior Alaska and heavy precipitation across the
Panhandle will be in the process of tapering off. Thereafter,
expect most areas to the north of the southern coast to trend
drier. After a brief lull, some moisture may return to the
southern coast/Panhandle for the latter half of the week,
depending on upper trough/surface low details. Best potential for
additional precipitation will be from the Panhandle to the
Southcentral coast. A Bering Sea wave may bring a period of
mostly light precipitation to the eastern Aleutians/Alaska
Peninsula on Tuesday. Northerly/northwesterly winds over the
eastern Aleutians/Alaska Peninsula should strengthen behind this
wave and its cold front, and the tightening surface gradient
between low pressure over the Gulf of Alaska and surface ridge
over the northern mainland will also raise the potential for
strengthening gap winds farther east along the southern coast
midweek. Thursday appears to be the day when the gap winds will
be the strongest as high pressure begins to build in from the
north while the Gulf of Alaska cyclone remains relatively strong.
The temperature forecast remains on track, with the early part of
the week featuring a west-to-east transition from above normal to
below normal readings. Well below normal temperatures (by at
least 20F over some areas) should cover much of the
western-central mainland by Wednesday, with perhaps some lingering
pockets of slightly above normal still over the North Slope and
southern Panhandle. Coldest anomalies should continue to nudge
eastward a bit during Thursday-Friday. While there are continued
uncertainties with the surface pattern over and near the Gulf by
mid-late week, ensemble guidance offers a very strong signal for
this episode of cold weather across much of the mainland.
Kong/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