Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
641 PM EDT Sun May 03 2020
Valid 12Z Thu May 07 2020 - 12Z Mon May 11 2020
...Guidance/Predictability Assessment...
Models/ensembles show relatively good consensus at the large
scales through the extended forecast period, with a persistent
trough/upper-level low south of Alaska across the North Pacific,
and an upper-level ridge axis building from western Canada into
mainland Alaska next week. This setup will eventually result in a
pattern resembling a Rex Block, that will persist through the end
of the extended forecast period. Even at smaller scales,
deterministic model consensus is above average during days 4-5
(Thu-Fri) as one low pressure system slowly weakens south of the
Gulf of Alaska and another weakens across the western Bering Sea.
The above average consensus during this time frame lent to the use
of a 12Z ECMWF/GFS blend during days 4-5. By days 6-8 (Sat-Mon),
the preferred storm track does not change substantially, but
guidance spread gradually increases through time with the next low
pressure system potentially approaching the western Aleutians by
Sat, although consensus on this system has improved a bit compared
to yesterday. Spread is highest days 7-8 with respect how this
surface low evolves over the western Bering Sea, and whether a
triple point low develops farther southeast closer to the
Aleutians. Given the decent large scale agreement, opted to
gradually increase weighting of ECENS/GEFS ensemble means through
time, with majority weight on the means by days 7-8.
...Weather/Hazard Highlights...
Persistent low pressure south of the Gulf of Alaska will keep
onshore flow and precipitation, along with gusty winds, in the
picture for the Alaska Peninsula and portions of southern mainland
Alaska through the forecast period, especially Thu-Fri as a
weakening frontal boundary approaches. The western/central
Aleutians will be subject to a couple rounds of rain and gusty
winds Thu and again Sat-Sun as frontal systems affect the region.
Rising heights across mainland Alaska as the upper ridge builds
will promote warming temperatures. High temperatures are forecast
to be 5 to 15 deg F above average across much of mainland Alaska
from the middle of the week into the weekend, with temperatures
forecast to rise into the 60s (possibly even approaching 70) for
portions of the Interior.
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