Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Thu Apr 25 2019
Valid 12Z Mon Apr 29 2019 - 12Z Fri May 03 2019
During the first half of the week there is relative agreement on
an amplified pattern as mainland ridging aloft builds northward
and troughing prevails over the Bering Sea. At the surface,
gradually weakening high pressure should prevail over the eastern
2/3 of the mainland and northeastern Pacific while strong low
pressure tracks northward over the western Bering. Flow to the
west of the surface high and wavy front extending from the Bering
low will provide some precipitation enhancement over the Alaska
Peninsula and eastern Aleutians.
By mid-late week there is a decent signal for an upper high to
close off and progress northward to some degree--perhaps leaving
some type of weakness over the mainland--while mean troughing
should exist between eastern Asia into the Bering but with a lot
of uncertain details. Flow around a Canadian upper low may push a
front into the Panhandle and eastern mainland.
For the mainland ridge aloft there has been a rapid trend toward
farther north progression of the closed high which ECMWF/GFS runs
and their means lift into the Arctic. Over the past day the
ECMWF/ECMWF mean have generally led this trend but there are still
minority solutions like the 00Z CMC/NAVGEM which do not lift the
upper high into the Arctic. The 12Z GFS adjusted more to the
ECMWF (and in fact exceeded it for a time around Wed) but the
ongoing spread favored a compromise approach among the 06Z GFS/FV3
GFS, 00Z ECMWF, and 06Z GEFS/00Z ECMWF means to provide a nudge
from continuity while awaiting confirmation of recent significant
trends. Even with the differences in specifics aloft among the
GFS/ECMWF runs and their means, there is a decent consensus at the
surface toward high pressure building over the Arctic relatively
lower pressure over the southern mainland.
Farther west a compromise (by way of the aforementioned model/mean
cluster) accounts for slower ECMWF trends closer to the GFS with
the Mon-Wed low over the Bering. Otherwise details from eastern
Asia across the Bering are not especially clear aside from the
area tending to be under mean troughing aloft. At the very least
there is a decent consensus suggesting that Bering/Aleutians
energy will not be as quick to reach the Gulf of Alaska as
depicted in the 12Z GFS.
Consistent with emphasizing operational model detail early and
accounting for increasing spread/uncertainty with time, the
forecast started with 80 percent total weight of 06Z GFS/FV3 GFS
and 00Z ECMWF guidance on day 4 Mon and then gradually
transitioned toward 70 percent total 06Z GEFS/00Z ECMWF ensemble
weight by day 8 Fri.
Rausch
Bullet points from the WPC Days 3-7 Hazards chart can be found at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
- High winds across portions of the Aleutians, Sun-Mon, Apr 28-Apr
29.
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