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FXAK02 KWNH 062321
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
721 PM EDT Sun Apr 6 2025

Valid 12Z Thu 10 Apr 2025 - 12Z Mon 14 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 late week into early next week, albeit
with model differences for embedded energies dropping south from
the Arctic and moving west to east through the northern Pacific.
Expect periods of moist mean southerly flow that could bring
modest amounts of rain and higher elevation snow into the southern
coast of the Mainland into Southeast Alaska. A surface low
pressure system tracking through the northern Pacific could also
spread rain showers to the Aleutians and Alaska Peninsula late
this week. Northerly to northwesterly gap winds may be brisk in
the vicinity of the Alaska Peninsula behind this low by next
weekend.


...Guidance/Predictability Assessment...

Model agreement is not ideal even for the beginning of the
forecast period Thursday regarding the position of upper lows
within the main trough. GFS runs for multiple days have
persistently shown an upper low staying just north of Alaska,
while another upper low is much farther south into the northern
Pacific, and south of other guidance. The southern upper low in
the GFS allows for a rather strong surface low toward Southeast
Alaska while other guidance was weaker. The GFS does have some
support from GEFS members for a deep surface low though, so will
continue to monitor, but continuing to lean away from that
solution seemed safer. A double barreled upper low into Thursday-
Friday still seems reasonable based on pretty good consensus from
the EC-based AIFS and the GFS-based Graphcast AI models, along
with the CMC today. The ECMWF and UKMET showed one dominant low,
but at least the placement seemed reasonable.

Guidance shows okay agreement regarding an upper and surface low
passing through the northern Pacific south of the Aleutians
Friday-Saturday. However, there may be some complex evolution of
this vort max interacting with additional shortwave energy
dropping from the Arctic through the trough by early next week.
This generally looks to produce an upper low near the Alaska
Peninsula or so, but models vary considerably with its placement.
Though the CMC was favorable for the start of the period, it
became west of consensus with its upper low position by Sunday.
The ECMWF meandered an upper low over the Y-K Delta to Seward
Peninsula. It may take some time for model guidance to come into
better alignment with this.

The WPC forecast used a blend favoring the CMC and some ECMWF and
UKMET and ensemble means early on. Lessened the proportion of the
deterministic models in favor of the ensemble means, with the
means reaching over half the blend by Day 6 and much more by Days
7-8, due to the increasing spread.


...Weather/Hazards Highlights...

Later this week, weak surface low pressure near the southern
coast of the Mainland should continue to focus coastal rain and
inland/higher elevation snow over the far south and Panhandle.
Rain and snow amounts should remain modest, but with some heavier
focus near Prince William Sound. Some areas of lighter and more
scattered precipitation (mostly snow) will extend farther north
over the Mainland. Upstream, possible shortwave energy could
spread light snow into the Y-K Delta late week into the weekend.
Meanwhile, North Pacific low pressure tracking eastward likely
just south of the Aleutians Friday and Alaska Peninsula Saturday
will allow for increasing precipitation chances and breezy winds
there. Combining energies aloft may lead to strengthening low
pressure in the Gulf. With a possibly deepening low, northerly to
northwesterly winds on the backside could be breezy to strong
across the Alaska Peninsula next weekend into next Monday.
Additionally, this could provide support for more precipitation,
with moderate to locally heavy amounts looking possible from the
Kenai Peninsula into Southeast Alaska for the weekend into early
next week. The details will continue to be refined in future
forecasts.

The upper trough forecast to be over the western Mainland through
much of the period will support below normal temperatures over
the western half or so of the state, but slowly moderating closer
to average. Meanwhile above normal temperatures are likely in the
East. The milder temperatures may expand westward by early next
week. Southeast Alaska looks to be near to a bit cooler than
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

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