Alaska Extended Forecast Discussion
National Weather Service College Park MD
619 PM EDT Sat May 24 2025

Valid 12Z Wed 28 May 2025 - 12Z Sun 01 Jun 2025

...General Overview...

Much of mainland Alaska will generally be sandwiched between two
upper-level gyres during much of the medium-range period. One
gyre rotating over the Arctic Ocean will send disturbances toward
the North Slope while the other gyre will continue to send
disturbances from the Bering Sea and North Pacific eastward toward
the Gulf of Alaska and the Alaska Panhandle. By late next week,
there is decent model agreement for a negatively-tilted upper
ridge to establish over mainland Alaska.


...Guidance Evaluation and Preferences...

With the presence of numerous smaller scale disturbances embedded
within the aforementioned two upper-level gyres, the
predictability of individual disturbances beyond Day 5 is lower
than normal. The largest model uncertainty appears to be located
just north of mainland Alaska where models are showing
difficulties in predicting the timing and location of a potential
closed low during midweek next week. This closed low/trough is
then forecast to lift back into the Arctic late next week, which
coincides with decent agreement for a negatively-tilted upper
ridge to establish over mainland Alaska. Meanwhile, models today
are indicating a better chance for a piece of the Arctic gyre to
develop into a smaller scale cyclone over the Bering Sea late
next week after passing through northeastern Siberia.

For the southern tier of Alaska including the Aleutians, models
are in good agreement for a number of disturbances/cyclones to
converge over the Gulf of Alaska next week followed by gradual
dissipation of the merger late next week. There is also decent
agreement shown by the ensemble means for the next cyclone to
reach the western Aleutians by next weekend, with the
deterministic solutions agreeing better with the ensemble mean
idea today.

The WPC forecast package today is based on the consensus of the
12Z ECMWF/00Z & 12Z EC mean (40%), 12Z GFS/06Z & 12Z GEFS (40%),
and 12Z CMC/CMC mean (20%) with ensemble means comprising the
vast majority toward the end of the forecast period. WPC
continuity is well-maintained.


...Weather/Hazards Highlights...

Periods of rain and high mountain snow are expected from the
Alaska/Kenai Peninsulas to the southeast Panhandle region, with
the greatest coverage and intensity expected from Juneau and
points south, where heavy rain appears most likely late Tuesday
through Thursday of next week, while heavy snow can be expected
for the high-elevations. Farther inland across the interior
section of mainland Alaska, scattered afternoon and evening
thunderstorms are likely to develop in the presence of an unstable
airmass, mainly between Anchorage and Fairbanks. There is a
tendency for these activities to expand toward northeastern Alaska
by late next week as southerly flow begins to establish under the
above-mentioned upper-level ridge. Lightning strikes from these
storms may increase the threat of wildfires in the region.

Temperatures overall are expected to be near to slightly above
average for late May standards across the central and southern
mainland, but slightly below normal north of the Brooks Range.
Cooler conditions are also likely for the coastal areas and the
near shore islands owing to increased cloud cover and rainfall.
Meanwhile, a slow warming trend is forecast for the entire Alaskan
domain as upper ridging is predicted to set in by next weekend
when June will be around the corner.

Kong


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