Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
646 PM EDT Fri Jul 17 2020
Valid 12Z Tue Jul 21 2020 - 12Z Sat Jul 25 2020
The forecast period begins on Tuesday with negative mid-level
height anomalies across northeastern Alaska associated with an
arctic upper low and trough situated northwest of the state, and
positive height anomalies over the Aleutians and also across
eastern Siberia. The influence of the arctic trough briefly
lessens into the middle of next week as the ridge axis attempts to
build in from the north Pacific across western Alaska. By the end
of the forecast period next weekend, it is appearing increasing
likely that another potent arctic trough will affect the northern
half of the state and heralding a potential pattern change.
Farther to the west, a well organized low pressure system over the
western Bering Sea on Tuesday is expected to drift slowly towards
the east and just north of the Aleutians through Friday.
The models indicate relatively good model agreement on Tuesday
with the exception of the CMC, which is more progressive with the
initial shortwave reaching southeastern Alaska early in the
forecast period. There appears to be above average model
agreement regarding the well developed low pressure system near
the Aleutians, with the GFS the most progressive solution.
Similar to yesterday, the ECMWF was quite strong with the arctic
surface low by the end of the forecast period, so it was used less
for the Thursday through Saturday period 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, along with some UKMET through Wednesday.
In terms of sensible weather, the best prospects for heavy
rainfall will be across the southeast Panhandle region on Tuesday
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 for much
of the week, with the potential for some sub-freezing low
temperatures north of the Brooks Range.
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, Monday, July 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