Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
610 PM EDT Mon Nov 01 2021
Valid 12Z Fri Nov 05 2021 - 12Z Tue Nov 09 2021
...Overview and Model Guidance...
Offshore storms will mainly affect coastal Alaska for the next
week. The flow will feature several potent Gulf of Alaska lows
rotating around a closed upper trough and as escaping Bering Sea
and Gulf of Alaskan impulses lift around the western periphery of
an amplified but slowly weakening western Canada to Alaskan
Interior upper ridge. Forecast spread has improved slightly over
medium range time scales and a blend of best clustered guidance
from the 12 UTC GFS/ECMWF (along with small smoothing inputs from
the GEFS/ECMWF ensemble means consistent with a pattern with near
normal predictability) seems to offer a reasonable solution for
days 4/5 (Friday-Saturday). Forecast spread increases more rapidly
after that and WPC blend weighting switches focus from the
GFS/ECMWF (for some detail consistent with below normal
predictability) to mainly the still compatible GEFS/ECMWF ensemble
means for days 6-8 (Sunday-next Tuesday). This forecast strategy
maintains decent WPC product continuity.
...Weather/Hazard Highlights...
A compact and moist extratropical low associated with former
Typhoon Malou is expected to lift from the eastern to northern
Gulf of Alaska Friday/Saturday and offer some focus for enhanced
precipitation into Southeast to south-central coastal Alaska.
Meanwhile, Bering Sea systems will combine with energies lifting
on the western periphery of an amplified Interior upper ridge
position to focus periods of enhanced precipitation into western
Alaska. In this pattern, the central and eastern Interior through
the North Slope should enjoy much above normal readings through
the weekend with some readings more than 20 degrees above normal
before moderating into next week. Meanwhile, deep energy digging
underneath into the Gulf of Alaska late week into early next week
will present a favorable environment for offshore storm genesis
with amplified/closed upper trough development to present a
periodic maritime and southern/southeastern coastal tier threat.
However, particular deep storm depiction at these longer time
frames remains uncertain given run to run guidance variance and
limited ensemble clustering.
Schichtel
Hazards:
- Heavy precipitation across the eastern portion of the Kenai
Peninsula, Thu, Nov 4.
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