Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
624 PM EDT Thu Apr 8 2021
Valid 12Z Mon Apr 12 2021 - 12Z Fri Apr 16 2021
***Atmospheric river event likely early next week***
...Guidance/Uncertainty Assessment...
The latest models and ensembles are in relatively good synoptic
scale agreement through the first half of the forecast period,
with the greatest differences residing with individual shortwave
perturbations pivoting around the main upper level low/trough over
the eastern Bering and northern Gulf region. One of the main
differences noted in the guidance is that the GEFS mean was more
out of phase compared to the well clustered CMC and EC ensemble
means beyond Tuesday across the Bering and Aleutians, and
generally less amplified with the upper trough/closed low over the
Gulf region. This also holds true for the operational GFS. The
latest runs of the ECMWF/CMC/UKMET are in better overall agreement
than the GFS, and therefore the WPC Alaskan product suite was
primarily derived from a blend of the 12Z ECMWF/CMC/UKMET/WPC
continuity through early Wednesday, and then mainly CMC/ECMWF/EC
mean for mid to late next week amid growing forecast spread.
...Weather/Hazards Highlights...
Temperatures across much of the Alaska domain should begin warming
up compared to the winter-like readings in the short range period
as the Arctic air mass retreats, and the negative temperature
anomalies abate. The latest model guidance is suggesting a return
to above normal readings across much of the central and northern
portions of the state by the middle of the week.
In the precipitation department, very heavy rain and mountain snow
is expected to make weather headlines from the Kenai Peninsula to
the southeast panhandle region. Multiple shortwave disturbances
pivoting around a broad upper level gyre over the Fox
Islands/eastern Bering will result in enhanced onshore flow across
this region. The potential exists for 6+ inches of QPF across
windward facing terrain, and one or more atmospheric rivers could
set up and result in flooding of low lying areas near the coast.
The higher elevations of the coastal mountain ranges could get
hammered by several feet of snow during the Tuesday-Thursday time
period.
Hamrick
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun-Wed, Apr
11-Apr 14.
- Much below normal temperatures across portions of mainland
Alaska, Sun, Apr 11.
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