Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
729 PM EDT Thu Jul 30 2020
Valid 12Z Mon Aug 03 2020 - 12Z Fri Aug 07 2020
...Guidance Evaluation...
The WPC Alaskan medium range product suite was mainly derived from
a composite blend of well clustered guidance from the 12 UTC
GFS/ECMWF/UKMET/Canadian models day 4/Monday. This solution is
also well supported by ensembles. Prefer to quickly transition to
a composite of 12 UTC GEFS/NAEFS/ECMWF ensemble mean solutions and
the 19 UTC National Blend of Models days 5-8 (Tuesday-next Friday)
amid growing forecast spread.
...Weather Highlights/Threats and Predictability...
A deep low slated to reach Bristol Bay and the Alaskan
Peninsula/Southwest Alaska by Monday/ will have closed upper
low/trough support and a strong model forecast signal. System
energy will transfer downstream into the northern Gulf of Alaska
into Tuesday/Wednesday and gradually fill, but enhanced wrapping
moisture and rain should spread earnestly over the region into
southern and southeast Alaska in less certain flow.
Upstream in this storm track, a second low on the heels of the
lead system may develop and work into the Southern Bering
Sea/Aleutians by midweek. WPC progs show a relatively modest low
due to uncertainty, but potential trough support aloft in this
stream and any phasing with northern stream trough energy dug
through the Bering Sea could favor stronger deepening. This low
may progress into Bristol Bay and the Alaskan Peninsula/Southwest
Alaska by next Thursday, then emerge into the again unsettled
northern Gulf of Alaska waters into next Friday. This system also
offers some potential for rainfall over southern and 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 southern
Alaska, Sun-Wed, Aug 2-Aug 5.
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