Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
633 PM EDT Tue Jul 14 2020
Valid 12Z Sat Jul 18 2020 - 12Z Wed Jul 22 2020
...Overview and Weather/Hazard Highlights...
The flow pattern across the North Pacific is forecast to become
gradually more amplified over the weekend and into early next
week, 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 arctic upper low
expected to affect the North Slope and portions of the Interior
this weekend, and another upper low forecast to dig south into the
western Bering Sea Sun through early next week. 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. Through time, cooler
temperatures are forecast to spread farther south across much of
mainland Alaska by by early next week. In the meantime, a low
pressure/frontal system is forecast to move east across the Gulf
of Alaska Sat as it weakens, with another similar system following
a similar track next Mon-Tue. These systems, and persistent broad
and unsettled onshore flow on the northern periphery of the upper
ridge will keep wet conditions in place through much of the
extended forecast period from the Alaska Peninsula to mainland
Alaska as well as Southeast Alaska.
...Guidance/Predictability Assessment...
Model/ensemble consensus has continued to show 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 heavily
weighted in the WPC forecast during days 4-5 (Sat-Sun). 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 (Tue-Wed). Ensemble consensus
in terms of the large scale flow pattern across Alaska and the
North Pacific was relatively good through day 8, with little in
the way of significant pattern changes indicated. Thus, forecast
confidence was average to slightly above average.
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
Hazards: No significant hazards are expected over Alaska during
this forecast period.
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