Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
543 PM EDT Wed Apr 07 2021
Valid 12Z Sun Apr 11 2021 - 12Z Thu Apr 15 2021
***Atmospheric river event likely early next week***
...Guidance/Uncertainty Assessment...
The latest models and ensembles are in relatively good synoptic
scale agreement through most of the 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. A shallow ridge is expected to
build across the mainland and western Canada through early in the
week, while an upper trough becomes established over the northern
Gulf. Similar to yesterday, recent runs of the ECMWF/CMC/JMA
remain better aligned with ensembles than the GFS, which is
stronger with shortwave energy across the Aleutians/Gulf region.
The UKMET was also less favored given a westward displacement with
the main surface low over the Bering as early as Monday.
Accordingly, the WPC Alaskan product suite was primarily derived
from a blend of the 12Z GFS/ECMWF/CMC/WPC continuity through
Tuesday, and some of the 12Z ECMWF/CMC and the GEFS/ECMWF ensemble
means for mid next week amid growing forecast spread.
...Weather/Hazards Highlights...
Temperatures across much of the Alaska domain should still be
quite cold going into Sunday with an Arctic surface high governing
the weather pattern over the weekend. The good news is a steady
moderation trend is forecast going forward into next weekend as
this 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 Wednesday and Thursday.
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 up to six inches of QPF
across windward facing terrain, and one or more atmospheric rivers
could set up and result in some 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
Monday-Thursday time period. Moderate to heavy snow is also
becoming more likely for portions of the Interior next weekend
owing to warm air advection.
Hamrick
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Wed, Apr
12-Apr 14.
- Much below normal temperatures across portions of mainland
Alaska, Sat-Sun, Apr 10-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