Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
737 PM EDT Fri Jul 31 2020
Valid 12Z Tue Aug 04 2020 - 12Z Sat Aug 08 2020
...Guidance Evaluation...
The WPC Alaskan medium range product suite was primarily derived
from a composite blend of now well clustered guidance from the 12
UTC GFS/ECMWF, 12 UTC GEFS/ECMWF ensemble means and the 19 UTC
National Blend of Models Tuesday-Thursday. Convergence of these
guidance pieces toward a more common solution bolsters forecast
confidence for this period. Quickly transitioned to a blend of the
now compatible 12 UTC GEFS/ECMWF ensemble means days 7-8 (next
Friday/Saturday) amid fast growing forecast spread. The 12 UTC
ECMWF ensemble mean has trended toward the GEFS for most features.
However, flow evolution/system development at high latitude over
the Arctic Ocean is quite uncertain and the ensemble mean blend
dilutes most features amid uncertainty.
...Weather Highlights/Threats and Predictability...
Energy with a deepened surface low under a supporting closed upper
low/trough will transfer downstream into the Northern Gulf of
Alaska Tuesday and gradually fill through Wednesday, but enhanced
wrapping moisture, wind and rain should spread earnestly into
southern/southeast Alaska. This storm will also present a maritime
hazard over the Gulf of Alaska.
Upstream, guidance has really come together compared to yesterday
in depiction of a second deep surface low and closed upper
low/trough on the heels of the lead system that is expected to
develop and work into the Southern Bering Sea/Aleutians
early-midweek. This low progresses into Bristol Bay and the
Alaskan Peninsula/Southwest Alaska Thursday, then emerges into the
again unsettled northern Gulf of Alaska waters next Friday and
Saturday. This system also offers potential for enhanced
wind/waves/rains along the track and downstream into
southern/southeast Alaska.
Schichtel
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, Mon-Tue, Aug 3-Aug 4.
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