Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
642 PM EDT Sat May 02 2020
Valid 12Z Wed May 06 2020 - 12Z Sun May 10 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 and
beyond the end of the extended forecast period. Even at smaller
scales, deterministic model consensus is above average during days
4-5 (Wed-Thu) as one low pressure system fills south of the Gulf
of Alaska and another weakens across the western Bering Sea. The
above average consensus during this time frame lent to use of a
12Z ECMWF/GFS blend during days 4-5. By days 6-8 (Fri-Sun), 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 late Fri into
Sat, with some solutions taking the low into the southern Bering
Sea and others keeping it farther south. 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 by Thu-Fri as a
weakening frontal boundary approaches. The western/central
Aleutians will be subject to a couple rounds of rain and gusty
winds Wed-Thu and again Sat-Sun as frontal systems affect the
region. Rising heights across mainland Alaska as the upper ridge
builds next week 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 next week into next
weekend, with temperatures potentially rising into the 60s 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