Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
635 PM EDT Mon Jul 13 2020
Valid 12Z Fri Jul 17 2020 - 12Z Tue Jul 21 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 arctic upper low expected to affect the
North Slope this weekend, 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. 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 Alaska
Peninsula 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. One additional aspect of
this pattern will be persistent onshore flow across Southeast
Alaska (on the northern periphery of the upper-level ridge), with
widespread showers this weekend and into early next week.
...Guidance/Predictability Assessment...
Model/ensemble consensus showed some improvement over recent days.
The 12Z ECMWF/CMC seemed to be the deterministic solutions most
well-centered within the overall consensus through much of the
extended forecast period. Thus, these solutions were heavily
weighted in the WPC forecast initially on day 4 (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 6-8 (Sun-Tue). 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