Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
621 PM EDT Mon Apr 26 2021
Valid 12Z Fri Apr 30 2021 - 12Z Tue May 4 2021
...Weather Pattern and Model Guidance...
The forecast period begins on Friday with a closed and elongated
upper low over western Alaska, a weakening trough over the Gulf,
and a large low passing south of the central/western Aleutians.
The upper low/trough lingers over the Alaska mainland going into
next weekend, followed by potential upper level ridging early next
week. Meanwhile, the Aleutian low should continue slowly eastward
near 45-50 degrees north and reach the northern Gulf by next
Monday, albeit a little weaker by this time.
The 12Z deterministic guidance agrees well on the overall synoptic
scale pattern through next weekend, and is an improvement compared
to the past couple of days. In terms of differences, the 12Z
ECMWF is faster with the Bering Sea/Gulf system by Monday compared
to the GFS/CMC solutions, and the ECMWF is slightly ahead of the
12Z EC mean. Similar to yesterday, the greatest uncertainty
resides across the Bering Sea and eastern Siberia regarding a
separate shortwave pivoting around the upper trough over western
Alaska, and how that eventually evolves. The WPC forecast leaned
toward a blend of the 12Z ECMWF/CMC/GFS/UKMET for the Friday
through Sunday time period, and then more of the EC/GEFS means
beyond that.
...Sensible Weather...
Temperatures are expected to be on the cool side for much of the
western half of Alaska under the influence of the upper level
trough and mostly cloudy skies, and near to slightly above normal
for portions of the North Slope and the eastern Interior. In
terms of precipitation, there will be two main rounds, with the
first round on Friday/Saturday associated with the weakening
disturbance from the northern Gulf region. The second round will
likely affect locations from the Alaska Peninsula to the southeast
Panhandle as the next storm system approaches from the Aleutians.
Hamrick
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle,
Thu-Fri, Apr 29-Apr 30.
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