Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
714 PM EDT Fri Jul 24 2020
Valid 12Z Tue Jul 28 2020 - 12Z Sat Aug 01 2020
...Overview and Guidance Evaluation...
Models and ensembles offer greater than normal forecast spread and
uncertainty for Alaskan and vicinity days 4-8. Continuity with
individual runs is not stellar either, but guidance does tend to
offer a reasonably similar larger scale pattern evolution.
Accordingly, the WPC Alaskan medium range product suite was
primarily derived from a blend of the 12 UTC GFS/ECMWF and
GEFS/ECMWF ensemble means along with the 19 UTC National Blend of
Models (NBM). Applied most weight to the ensemble means and NBM
throughout the period to maintain max WPC continuity and to smooth
out the less predictable small-mid scale features. This was
coordinated with Alaskan offices and the resultant product still
highlights several organized weather features noted below.
...Weather Highlights/Threats...
Deep layered Arctic low passage should hold a frontal zone down
over northern Alaska for much of next week. Frontal wave
progression from the west will favor enhanced moisture and
precipitation for the Brooks Range and vicinity into Tue, with
unsettled conditions likely to linger but moderate later next week.
Deepened North Pacific to Aleutians/Southern Bering Sea low
progression will focus rainfall and waves/winds across the region
next week. Lead low energies with ample closed upper low/trough
support in an amplified pattern Tue-Thu will tend to transfer into
an unsettled Gulf of Alaska Thu-next Sat. Upstream flow seems
sufficiently amplified and favorable to bring new low pressure
systems back into the Aleutians and Bering Sea into Thu-next Sat,
but predictability at these longer time frames is low.
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 Brooks Range and interior
southeastern Alaska, Mon-Tue, Jul 27-Jul 28.
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