Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
730 PM EDT Sat Jul 24 2021
Valid 12Z Wed Jul 28 2021 - 12Z Sun Aug 01 2021
...Guidance/Predictability Evaluation...
The latest ensemble means from the ECMWF, GFS, and CMC agree
reasonably well with the synoptic evolution across Alaska through
Day 8. It appears that a general model compromise together with
their deterministic solutions should work well as a starting
point. This will keep the relatively deep low lingering and then
slowly weakening over eastern Siberia into late next week. By
later next weekend, the 12Z ECMWF is bringing a deeper cyclone
into the Bering Sea, possibly after ingesting some moisture from
T.S. Nepartak. On the other hand, the GFS tends to be the fastest
solution with regard to bringing the associated upper trough from
the Bering Sea towards western Alaska as a surface low pressure
wave develops and heads towards the West Coast. This scenario is
depicted in the 12Z CMC as well. The WPC Alaskan forecast package
for Days 7-8 leans towards to slower ensemble means solutions,
which would keep a slightly stronger ridge over southern Alaska
next weekend. A general even blend of the 12Z ECMWF/00Z EC mean,
12Z GFS/12Z GEFS, together with some contributions from the 12Z
CMC/CMC mean was adapted for Days 4-6.
...Weather/Threats Highlights...
The main areas of precipitation and unsettled weather will be
focused across the western and northwestern mainland throughout
the period as southerly flow ahead of the Bering Sea cyclone
interacts with a stalled stationary boundary across the North
Slope. The best chance for heavier precipitation will be Tuesday
and Wednesday across parts of the Seward Peninsula, and northward.
Moderate to locally heavy rains may continue after Wednesday, but
confidence in the amounts and particular locations remains low at
this time. High waves and gusty winds may also present themselves
near the West Coast. The next developing cyclone moving into the
Bering Sea and Aleutians later in the week could lead to some
higher waves and precipitation for parts of the Aleutians
especially by next weekend. For western and northern parts of
Alaska, temperatures should remain below normal, but should trend
warmer for eastern parts of the state as upper level ridging
builds in aloft.
Kong/Santorelli
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