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FXAK02 KWNH 052327
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
727 PM EDT Sat Apr 5 2025

Valid 12Z Wed 09 Apr 2025 - 12Z Sun 13 Apr 2025


...Overview...

Mean upper troughing is forecast to stretch from the Arctic
southward through the western and central Mainland and into the
northeast Pacific through the period into next weekend, albeit
with model differences for embedded upper lows. This pattern will
allow for cooler than average temperatures across western Alaska
that should moderate somewhat as the week progresses.
Additionally, the mean southerly flow causes some moisture to feed
into the southern coast of the Mainland into Southeast for
precipitation chances, with modest amounts of rain and higher
elevation snow that gradually lessen into late week. Upstream, a
low pressure system looks to pass south of the Aleutians and the
Alaska Peninsula late week into next weekend could spread some
rain showers and perhaps gusty winds to those areas.


...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 Wednesday. GFS runs for the past couple of days
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.
While a double barreled upper low seems reasonable based on pretty
good consensus from the EC-based AIFS and the GFS-based Graphcast
AI models, and from the ICON, the large separation between the
upper lows like GFS runs have was not favored. Additionally, at
the surface the 12Z GFS brought a rather strong low toward
Southeast Alaska while other guidance was weaker and/or farther
south. The GFS does have some support from GEFS members though, so
will continue to monitor, but leaning away from that solution
seemed safer for now. Meanwhile, the ECMWF and CMC indicate one
upper low in between the potential southern and northern lows, but
blending in some UKMET that had an upper low on the northern side
produced a somewhat reasonable solution. Overall used a blend of
the UKMET, CMC, and ECMWF and ensemble means through the period,
gradually ramping up the proportion of ensemble means to over half
by late week into next weekend. This also worked for the system
upstream as vorticity feeds eastward with a surface low tracking
likely south of Alaska through the northern Pacific. The 06Z GFS
in particular seemed like an outlier in bringing energy forming an
upper low to the north of the Aleutians into the Bering Sea.


...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 gradually taper off from early week higher amounts
as Gulf surface low pressure weakens. Modest amounts of
precipitation are likely to focus from Prince William Sound toward
Yakutat especially Wednesday-Thursday. Some areas of lighter and
more scattered precipitation (mostly snow) will extend farther
north over the Mainland. The overall pattern should produce brisk
northwesterly winds over and near the Alaska Peninsula that could
continue into Wednesday, but are not expected to rise to hazardous
levels. Then upstream, North Pacific low pressure tracking
eastward likely just south of the Aleutians and Alaska Peninsula
will allow for increasing precipitation chances and breezy winds
there. Light snow is possible in the Y-K Delta to Interior with
shortwave energy next weekend as well.

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 into Wednesday, and slowly moderating closer to normal
for later week. Meanwhile above normal temperatures are likely in
the East. By Friday and into the weekend temperatures should be
generally closer to average, though with the same overall pattern
of cool in the West and milder in the East.


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

$$