Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
615 PM EDT Sun Jul 4 2021
Valid 12Z Thu Jul 8 2021 - 12Z Mon Jul 12 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 southern portions of the state for the
end of the week, and then the core of the upper low should
gradually settle south over the northern Gulf by next weekend
while the polar vortex remains strong over the Arctic and this
will support a frontal boundary near the Arctic Coast. A narrow
upper ridge axis may try to build in between these two features
across portions of the Interior for next weekend and into next
Monday.
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. The extent of
the upper level ridging over north-central Alaska is a bit less
certain. In terms of model preferences, the WPC forecast was
primarily derived from a deterministic model blend through Friday,
and then more of the ensemble means for next weekend and Monday.
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 through Saturday, 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 to
close out the week across the favored windward terrain. Showers
are also expected to be scattered 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