Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
323 PM EDT Sun May 19 2019
Valid 12Z Thu May 23 2019 - 12Z Mon May 27 2019
Models have come into somewhat better agreement during the first
part of the extended period. The consensus has trended toward the
idea of keeping a relatively strong upper ridge in place across
the Gulf of Alaska, and keeping a broad upper trough farther west
across the Aleutians/North Pacific for longer. Thus, expect one
weakening low pressure system to be crossing the eastern Bering
Sea/Alaska Peninsula on Thu, with another system following about
1-2 days behind it, approaching the eastern Aleutians/Alaska
Peninsula by Fri-Sat. Given somewhat improved consensus, the
forecast during days 4-5 was based on a multi-model deterministic
blend including the 00Z ECMWF/CMC and 06Z GFS.
After day 5, ensembles show general agreement on the large scale
pattern, with the upper trough gradually sliding east and breaking
down the northern extent of the upper ridge. Differences become
quite significant, however, with respect to the details of
individual systems traversing the broader mean trough. Thus,
trended heavily toward the ECENS/NAEFS ensemble means during days
6-8 (Sat-Mon), which supported the idea of another low pressure
system crossing the western/central Aleutians during that time
frame, as the system farther east reaches southern mainland Alaska
and weakens in the anticyclonic flow on the northern periphery of
the upper ridge.
Ryan
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