Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
620 PM EDT Sat Jul 3 2021
Valid 12Z Wed Jul 7 2021 - 12Z Sun Jul 11 2021
...Overview and Guidance/Predictability Evaluation...
A rather amplified and slow moving pattern is expected to exist
across the Alaska domain for the medium range forecast period. A
deep upper level trough with embedded closed low should remain
anchored in place across western and central portions of the
state, and then the core of the upper low should gradually settle
south over the northern Gulf while the polar vortex remains strong
over the Arctic and this will support a frontal boundary near the
Arctic Coast. An upper level ridge over west-central Canada will
tend to keep the pattern from changing too much.
The deterministic models and the ensemble means are in generally
above average agreement on the synoptic scale pattern through most
of the forecast period, with some timing differences on some of
the individual shortwaves pivoting around the main upper level
gyre over the Alaska Peninsula and northern Gulf. In terms of
model preference, the WPC forecast was primarily derived from a
deterministic model blend through Friday, and then more of the
ensemble means for next weekend. Some previous WPC continuity was
also maintained through day 7.
...Weather/Threats Highlights...
Given the broad upper low/trough in place, increased cloud cover
and widespread showers will tend to keep temperatures below
average across most of the state, with the greatest anomalies
likely for south-central Alaska with highs running up to 20
degrees below normal. Readings should slowly return closer to
average by the end of the forecast period. Another thing to
monitor is the prospect for moderate to heavy rainfall from the
Alaska Peninsula to western portions of the southeast Panhandle,
where 1-3 inches of rain will be possible. Showers are also
expected to be scattered to numerous during the afternoon hours
across portions of the Interior as well. Gusty winds can also be
expected for southern coastal regions with the unsettled weather
pattern in place across the northern Gulf region.
Hamrick
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
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