Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
740 PM EDT Fri Apr 4 2025

Valid 12Z Tue 08 Apr 2025 - 12Z Sat 12 Apr 2025


...Overview...

Mean upper troughing is forecast to stretch from the Arctic 
southward through the western Mainland and into the northeast 
Pacific next week, albeit with model differences for embedded 
upper lows. This pattern will allow for cooler than average 
temperatures across western Alaska that may moderate somewhat as 
the week progresses. Additionally, some moisture will feed into 
the southern coast for precipitation chances, with modest amounts 
of rain and higher elevation snow that could gradually lessen 
later in the week. A low pressure system looks to pass south of 
the Aleutians late next week but could spread some rain showers 
there.


...Guidance/Predictability Assessment...

Models continue to vary significantly regarding the position of
upper lows within the main trough, even at the start of the
forecast period Tuesday. GFS runs since at least yesterday have
persistently shown an upper low staying just north of Alaska that
is the dominant feature, with a weaker upper low farther south
into the northern Pacific, and south of other guidance. Meanwhile
the ECMWF indicates an upper low quickly dropping south across the
western Mainland. The CMC and UKMET show an intermediate position
in between the northern GFS and southern ECMWF Tuesday-Wednesday.
The CMC in particular does show two embedded lows, which matches
reasonably well with the EC-based AIFS and the GFS-based
Graphcast. Plus its latitudinal position seemed favorable compared
with the CMC/EC ensemble means. Thus the WPC forecast, like
yesterday, did not favor the GFS/GEFS guidance even early in the
period. Instead a blend of the CMC, ECMWF, UKMET (from most to
least) plus some CMC and EC ensemble means were used. Did think
that by Thursday the CMC stalled the upper low a bit too long atop
the Y-K Delta while the majority of guidance had the low south by
then. Thus gradually ramped up the proportion of ensemble means to
half Day 6 and more Days 7-8. This also worked for the late period
as the upper low drifts east through the northern Pacific (GFS
runs were not favored as too far south and east) and for
additional energy coming near the Aleutians (GFS runs farther
north than non-NCEP guidance).


...Weather/Hazards Highlights...

Upper dynamics and surface low pressure near the southern coast 
of the Mainland should continue coastal rain and inland/higher 
elevation snow over the far south and Panhandle. The precipitation
is forecast to be heaviest early in the week and gradually taper 
off as Gulf surface low pressure weakens. One more day of heavy 
precipitation is indicated on the Day 3-7 Hazards chart for Monday
especially considering the wet antecedent conditions by then. 
Some areas of lighter and more scattered precipitation (mostly 
snow) may extend farther north over the Mainland. Additionally, a 
shortwave and a surface wave moving through the Y-K Delta and 
vicinity could bring light snow there and into the Alaska 
Peninsula into Tuesday. The overall pattern should produce brisk 
northwesterly winds over and near the Alaska Peninsula especially 
through Tuesday, but with speeds likely staying below hazardous 
criteria. The Aleutians could see some influence from North 
Pacific low pressure by later week, with increasing rain chances 
and breezy winds.

The upper trough forecast to be over the western Mainland through
much of the period will support below normal temperatures 
(especially for highs) over the western half or so of the state 
especially Tuesday-Wednesday, and slowly moderating closer to 
normal for later week. Meanwhile above normal temperatures are 
likely in the East. By Friday-Saturday temperatures should be 
generally closer to average.


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