Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
631 PM EDT Mon Jul 5 2021
Valid 12Z Fri Jul 9 2021 - 12Z Tue Jul 13 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
strong shortwave trough settling southward across western Alaska
early in the forecast period should evolve into a closed low in
the general vicinity of the Alaska Peninsula by Saturday, and then
settle southward over the northern Gulf by Sunday and into Monday.
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 the exception of the Arctic where
more significant timing differences on shortwaves exists. 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
Saturday night, for early next week while still maintaining some
of the CMC/ECMWF/GFS. 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 10 to 20 degrees below normal, particularly across western
and southern portions of the state. A moderation trend should
commence by the Sunday to Tuesday time period as the weak upper
ridge builds in across much of the Interior.
Another thing to monitor is the prospect for episodes of heavy
rainfall from the Alaska Peninsula to western portions of the
southeast Panhandle, with the potential for some 2-4 inch rainfall
totals with locally higher amounts. This would be in response to
enhanced onshore low-mid level flow ahead of the closed upper low,
with a potential atmospheric river setting up this weekend near
the Kenai Peninsula. Showers are also expected to be scattered
during the afternoon hours across portions of the Interior as
well. Gusty winds are likely for southern coastal regions with
the unsettled weather pattern in place across the northern Gulf
region.
Hamrick
Hazards:
- Heavy rain across portions of the Alaska Panhandle and southern
mainland Alaska, Sat-Mon, Jul 10-Jul 12.
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