Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
506 PM EDT Sun Oct 31 2021
Valid 12Z Thu Nov 04 2021 - 12Z Mon Nov 08 2021
...Overview and Model Guidance...
A pattern with potent offshore storms will continue to affect
portions of Alaska for the coming week. The flow will feature
several potent Bering Sea and Gulf of Alaskan lows rotating within
energetic/closed mean upper troughs over these areas and around
the periphery of an amplified western Canada to Interior mean
upper ridge. Guidance continuity and variance with embedded
features remains less than stellar throughout medium range time
scales, but a blend of best clustered guidance from the 12 UTC
GFS/ECMWF/Canadian/UKMET does offer a seemingly reasonable
solution that despite many messy smaller scale system differences
maintains decent larger scale WPC product continuity day 4 into
day 5 (Thursday into Friday). Forecast spread rapidly increases
after that and WPC guidance quickly turns to the more smoothed but
more compatible GEFS/ECMWF ensemble means later Friday into days
6-8.
...Weather/Hazard Highlights...
A lead extratropical low partially associated with recent western
Pacific Typhoon Malou will lift to the northern Gulf of Alaska
Wednesday into Thursday. This offers some threat for maritime
interests and inland as heavy precipitation works from southeast
through southern Alaska and the AKpen/Kodiak Island. There is now
an increasing guidance signal that another low linked to Malou may
also lift into the Gulf of Alaska or western Canada Friday,
perhaps into Saturday to offer a less certain focus for heavy
precipitation. Meanwhile, additional storm systems will also into
this period work from the Bering Sea and combine with energies
lifting on the western periphery of an amplified Interior upper
ridge position to spread 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
this week, with many locals more than 20 degrees above normal.
Deep energy digging underneath into the Gulf of Alaska late week
through next weekend into early next week may also present a
favorable environment for storm genesis with amplified/closed
upper trough development to present a multi-day maritime and
southern and southeastern coastal tier threat. However, particular
deep storm depiction at these longer time frames, as now most
evident in the 12 UTC GFS, is quite uncertain given run to run
guidance variance and limited ensemble clustering.
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