748
FXAK02 KWNH 132309
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
709 PM EDT Mon May 13 2024

Valid 12Z Fri May 17 2024 - 12Z Tue May 21 2024

...Guidance Evaluation and Preferences...

As early as this weekend there is a lot of uncertainty in the
overall flow pattern across Alaska into early next week. Friday
into Saturday, there is general consensus that an amplified trough
will split sending a shortwave across northern Alaska and another
into the Gulf. The GFS is the major outlier here with a much
stronger and faster Gulf of Alaska system. The UKMET was different
as it brought the northern stream energy south into the Bering
with a deep closed low and little to no support from any other
guidance. The early period blend was heavily based on the better
agreeable ECMWF and CMC, with the ensemble means. This also had
support from the ECMWF-initialized ML models as well.

After Saturday and into next week, uncertainty in the pattern
evolution over Alaska significantly increases. There is some
general consensus that at least weak ridging should build behind
the early period Mainland troughing, along with a weak shortwave
moving into the Bering Sea. The ECMWF has been fairly consistent
in this shortwave amplifying as it moves into the Mainland early
next week, while the GFS suggests it shifts more northward and
weakens towards the Bering Strait as strong ridging builds over
the Mainland/Gulf. A quick look at the ensembles and ML models
shows better support for some sort of ridging or flatter flow, but
there is a considerable amount of spread lending to a very low
confidence forecast. However, given no clear guidance on which
deterministic solution may be more plausible, the WPC Alaska blend
for today trended significantly towards the ensemble means, but
did incorporate back in some of the GFS just for a little bit of
added definition. The next system will move across the western
Aleutians around Monday-Tuesday but with some discrepancies in
timing.


...General Overview and Weather/Hazards Highlights...

A weak surface low into the Gulf Friday-Saturday should allow for
some general light to moderate rainfall along the coast. Mean low
pressure across the Mainland should also result in light showers
through the weekend and maybe into next week farther inland as
well. Total rainfall along the coast should be on the order of
maybe 1-2 inches, which would not reach hazards level criteria.
Upper ridging building in behind this initial system would help
the Southern Coast/Southeast region dry out some going into next
week. A cold front will also begin spreading showers from west to
east across the Aleutians by next Monday.

Western to southern Alaska should be modestly below normal to
start the period underneath amplified ridging. By the weekend and
beyond, temperatures should regulate back towards normal but still
cool. The Eastern interior and North Slope will be 10-20 degrees
above normal for this time of the year, but should gradually shift
back towards normal by next week.


Santorelli


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

$$