Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
642 PM EDT Sun Jul 12 2020
Valid 12Z Thu Jul 16 2020 - 12Z Mon Jul 20 2020
...Overview and Weather/Hazard Highlights...
The flow pattern across the North Pacific is forecast to become
gradually more amplified during the extended forecast period, with
an upper trough strengthening from the Bering Sea south across the
Aleutians, and an eastern Pacific ridge attempting to make some
headway northward into the Gulf of Alaska. The amplifying flow
will allow for increasing potential for arctic upper-level energy
to move southward, with an upper low expected to move south toward
the North Slope Fri-Sat, and another upper low forecast to dig
south into the western Bering Sea Sun-Mon. The primary impact of
the system affecting the North Slope will be on temperatures, with
colder temperatures spreading across the region, and highs
forecast to be 10-20 deg below average. In the meantime, a low
pressure/frontal system is forecast to move east across the Alaska
Peninsula Thu-Fri as it weakens, with another frontal wave
following quickly behind it by Sat. These systems will keep rounds
of showers in the picture from the Aleutians east into southern
mainland Alaska from late this week into the weekend, with some
potential for gusty winds at the coast. Shower activity may also
be enhanced by Fri-Sat across portions of the Interior as moisture
interacts with a weak stationary front.
...Guidance/Predictability Assessment...
Model/ensemble consensus showed some improvement over recent days.
The 12Z ECMWF seemed to be the deterministic solution most
well-centered within the overall consensus through much of the
extended forecast period. Thus, the ECMWF was heavily weighted in
the WPC forecast during days 4-5 (Thu-Fri). After that, a gradual
trend toward heavier weight on ensemble means (ECENS/NAEFS) was
shown through time, with ensembles comprising a majority of the
forecast by days 7-8 (Sun-Mon).
Ryan
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