Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
539 PM EST Thu Feb 25 2021
Valid 12Z Mon Mar 01 2021 - 12Z Fri Mar 05 2021
...Robust Bering Sea/Aleutians system Monday...
...Overview and Guidance/Uncertainty Assessment...
The medium range period will be driven by a strong upper positive
height anomaly moving off Hokkaido this weekend (+3 to +3.5 sigma
500mb heights per the ECMWF ensemble mean) and into the Bering Sea
by the middle of next week. This will favor downstream robust yet
progressive troughing out of the Bering ahead of the ridge into
the Gulf of Alaska in general west-to-east flow. With a rather
defined wavelength, the models/ensembles were in good to very good
agreement overall. A blended deterministic solution was utilized
for the first few days of the period Mon-Wed (12Z
GFS/ECMWF/Canadian/UKMET) in order to capture the depth of the
Bering low Monday and as it made its way to the Gulf of Alaska
well behind the surface front. By next Thu/Fri, GFS/ECMWF paired
well enough with their ensemble means (and each other) to use a
majority of their agreement to define the next system into the
Bering as the Gulf low slowly weakens. The 12Z parallel version of
the GFS was preferred over the operational version due to its
better handling of lead-in flow south of the Gulf and upstream
system tracks. Upper pattern may flatten by next weekend
suggesting lower predictability.
...Weather/Hazards Highlights...
Bering system on Monday will bring windy conditions to the region,
mostly over the Aleutians, with 50kts possible across the island
chain and 60kts over the open waters around the low. Precipitation
will be light to modest due to the progressive flow. As it moves
through the Panhandle, another round of rain/snow is likely for
areas that have seen an active pattern. Light to moderate snow
will spread across southwestern areas ahead of the occlusion and
around the trailing surface low. Precipitation will then again
focus on the Panhandle for the end of the week as the upper trough
digs into/through the Gulf. Temperatures will generally be below
normal over much of the state next week, focused over the
western/southwestern portion of the state as the upper low moves
through.
Fracasso
Hazards:
- High winds across portions of mainland Alaska and the Aleutians,
Sun-Mon, Feb 28-Mar 1.
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