Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
409 PM EDT Sun Sep 26 2021
Valid 12Z Thu Sep 30 2021 - 12Z Mon Oct 04 2021
...Three Major Storms for Alaska over the next week...
...Guidance/Predictability Assessment and Pattern/Hazard
Highlights...
A very stormy pattern for Alaska and offshore waters continues and
forecast predictability remains above average overall. However,
despite a reasonably well clustered 500mb flow evolution in the
models, vorticity interactions and phasing issues have led to more
offshore surface low differences than was the case yesterday. I'd
prefer to flip the script from yesterday and instead blend the
model supportive and quite compatible GEFS/ECMWF ensemble means
for the entire WPC day 4-8 forecast period for max consistency.
WPC product continuity was well maintained in this manner in
conjuncture with manual surface system modifications to ensure
sufficient offshore storm depth/intensity consistent with a highly
supportive and amplified upper flow evolution as a series of
powerful closed lows/troughs work through the Bering Sea and into
the Gulf of Alaska.
A lead storm system will bring a threat of high winds/waves across
the Gulf of Alaska into Thursday, allowing a southwesterly push of
moisture to funnel especially into the Panhandle where rainfall
amounts may be locally heavy in the valleys (and snow at the
higher elevations). Meanwhile, a dangerous storm system
digging/consolidating through Bering will robustly dig to bring
high winds/waves along with an enhanced rain/snow to western then
southwestern areas of the mainland. Into later next week as the
system slams into the highly unsettled Gulf of Alaska, another
round of potentially heavy rain/snow are expected for the
Panhandle and coastal areas of south-central Alaska. Temperatures
will overall generally be below normal for the period due to the
continued troughing over much of the state. Farther upstream,
powerhouse Typhoon Mindulle will start to recurve into the
westerlies from the south of Japan by midweek. After that, the
ensemble consensus takes the system to the northeast into/toward
the trough to its north/northeast. A deep extratropical low
associated with Mindulle is slated to track toward the southwest
Bering Sea next weekend into early next week as a maritime and
Aleutians heavy seas/wind/rainfall threat.
Schichtel
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