Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
614 PM EDT Thu Jul 16 2020
Valid 12Z Mon Jul 20 2020 - 12Z Fri Jul 24 2020
The forecast period begins on Monday with a corridor of negative
mid-level height anomalies across the northern half of Alaska
associated with an arctic trough draped across the region, and
positive height anomalies near the southeast Panhandle region and
also across eastern Siberia. The influence of the arctic trough
lessens through next week as the ridge axis attempts to build in
from the north Pacific. Farther to the west, a well organized low
pressure system over the western Bering Sea on Monday is expected
to drift slowly towards the southeast, and be over the vicinity of
the western Aleutians by the end of next week, with its eastward
progression limited by the ridge axis that will likely to be over
the southwest Alaska mainland.
The models indicate the greatest differences regarding flow across
the Gulf of Alaska region, with the CMC more progressive with the
initial shortwave reaching southeastern Alaska early in the
forecast period, and the GFS is more progressive with the
following shortwave trough. There appears to be above average
model agreement regarding the well developed low pressure system
near the Aleutians, with the CMC and GFS slightly ahead of the
ensemble means. The ECMWF was quite strong with an arctic surface
low by the end of the forecast period with little in the way of
ensemble support, so it was used less for next Thursday and Friday
for the northern third of the state. Elsewhere, a
ECMWF/GFS/GEFS/EC mean blend was incorporated as a starting point
in the forecast process for fronts and pressures.
In terms of sensible weather, the best prospects for heavy
rainfall will be across the southeast Panhandle region early in
the week as steady onshore flow advects a plume of enhanced
moisture towards the terrain, with the potential for 1 to 2+
inches through Tuesday night. The second area of noteworthy rain
will be across portions of the Aleutians in association with the
surface low originating from the western Bering Sea, but not to
the same magnitude as the first system farther east. Temperatures
will likely be below normal for the northern third of Alaska
through mid-week, with the potential for some sub-freezing low
temperatures north of the Brooks Range. A moderation trend is
expected to commence with readings returning to near normal or
slightly above for most of the state by the end of the week.
Hamrick
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
Hazards: Heavy rain across portions of the Alaska Panhandle and
southern mainland Alaska, Sun-Mon, July 19-20.
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