Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
702 PM EDT Mon Apr 19 2021
Valid 12Z Fri Apr 23 2021 - 12Z Tue Apr 27 2021
...Overview and Guidance/Uncertainty Assessment...
Latest guidance continues to depict a fairly blocky regime during
much of the extended range period, with upper ridging dominating
much of mainland Alaska. The period begins Friday with one system
moving through the N. Pacific towards the Northwestern U.S. coast
as a couple of closed lows/systems make their way towards the
Aleutians. By Sunday/day 6, the pattern should consolidate into
one main low just south of the central/eastern Aleutians with an
organized low pressure system at the surface. After this, models
begin to diverge on the evolution and track of this low, related
to how quickly the ridge wants to break down over the mainland.
Contrary to previous days, the 12z GFS is now the quickest to
break down the ridge which pulls the Aleutians low north into the
Bering Sea days 7-8. The 12z ECMWF/CMC both suggest the ridge
holds strong and forces the low eastward towards the N. Pacific
(also with support from the ensemble means). The WPC forecast for
today used a composite blend of mostly 12z GFS/ECMWF/CMC through
day 6. For days 7 and 8, removed the GFS from the blend in favor
of more ensemble mean contribution as well as smaller percentages
of the ECMWF/CMC for added detail and system definition. This
approach fits well with yesterdays continuity as well as the
preference downstream over the CONUS.
...Weather/Hazards Highlights...
Most of Alaska should remain warm and dry through the period, with
any precipitation confined to the Aleutians/Alaska Peninsula and
vicinity, particularly associated with the low pressure system
Sunday into Monday as it drifts over or just south of the islands.
Light to moderate amounts are most likely, though some locally
higher totals could be possible depending on exact strength and
track of the low. A period of gusty winds are also likely in
associated with this storm.
The vast majority of the state should be well above normal in
terms of temperatures through much of the period, with the warmest
anomalies over the North Slope region and western areas of the
Mainland (with even more anomalous warm morning lows). Lowering
heights across eastern Alaska early next week should help to
moderate temperatures a bit back towards normal or even below. The
exception to all this warmth will be in the southeast quadrant and
much of the Panhandle where temperatures should be near or below
normal the entire medium range period.
Santorelli
Hazards:
-Much above normal temperatures across portions of mainland
Alaska, Thu-Mon, Apr 22-Apr 26.
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