Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
348 PM EDT Mon Sep 16 2019
Valid 12Z Fri Sep 20 2019 - 12Z Tue Sep 24 2019
The guidance continues to show an active northern Pacific stream
which features two dominant storm systems tracking along or just
south of the Aleutians and then into the Gulf of Alaska. These
systems will likely bring some enhanced rainfall to the
Aleutians/Alaskan Peninsula and support much heavier precipitation
at times over the southeastern coast/Panhandle. Model and
ensembles continue to highlight the southeastern coast/Panhandle
region for the highest five-day precip totals (on the order of 5+
inches). Meanwhile, an upper low (with one or more individual
impulses) should meander somewhere between the northwestern
mainland coast and eastern Siberia which would support below
normal temperatures by this weekend and potential for rain/snow
mix across the North Slope/interior Alaska, with snow possible in
the higher terrain.
Models show good agreement on the first system tracking from the
Peninsula to the Southern Coast Friday-Saturday and eventually
weakening over southeast AK on Sunday. The second system should
move along or just south of the Aleutians Saturday-Sunday, and
into the Gulf on Sunday. There remains some disagreement on timing
with this system, with the GFS/GEFS suite a bit slower than the
ECMWF/ECENS. The 00z CMC sat somewhere in the middle of the two.
Across Northern AK, there is fairly good synoptic agreement on a
meandering upper low, with normal detail/timing differences
arising later in the period. Across the board, the WPC forecast
uses a blend of the 12z GFS/00z ECMWF/00z CMC for days 4-5, with
increasing ensemble mean contributions days 6-8. This results in a
good middle ground solution for the second Aleutians/Gulf low and
fairly modest changes/refinements versus continuity.
Santorelli
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Fri-Sat, Sep 20-Sep 21.
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