Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
728 PM EDT Fri May 1 2020
Valid 12Z Tue May 5 2020 - 12Z Sat May 9 2020
...Expected weather pattern and model overview...
There is a good signal in the medium range guidance for a Rex
block pattern to develop over the north Pacific and the Alaska
mainland next week, with an upper level ridge extending northwest
from British Columbia and the Yukon, and a broad upper level gyre
over the Gulf of Alaska with a couple of low pressure systems
passing south of the region. Another ridge axis is likely to
exist near the central Aleutians with an upper trough over eastern
Siberia.
Relatively good agreement exists between the 12Z GEFS mean and the
12Z ECENS through about Thursday, after which the GEFS becomes
much stronger with the ridge developing south of the Aleutians.
The CMC and its ensemble mean indicate significant placement
differences with both the Aleutians ridge and Gulf low displaced
to the east of the model consensus. By Thursday night and
especially into Friday, the ECMWF becomes much stronger with an
upper low over the western Bering Sea that has only very limited
support from its ensemble mean. There was enough synoptic scale
agreement through Wednesday to merit a blend of the
UKMET/ECMWF/GFS and some ensemble means, and then more of the
ECENS with some GEFS and previous WPC continuity for the Thursday
through Saturday time period.
...Sensible Weather...
Most of central and northern Alaska is expected to be dry through
Wednesday with the best rainfall prospects confined to the eastern
Aleutians, southeast Panhandle, and the southern third of the
mainland as low pressure over the Gulf of Alaska advects moisture
inland. Some lingering below average temperatures are likely from
the Brooks Range northward through midweek, and potentially well
above normal readings for western portions of the Interior. These
warm anomalies will probably persist through the entire medium
range period for central and southern portions of the state with
the upper level ridge axis building in from western Canada. This
will likely accelerate melting snow for many areas. By the end of
next week, there may be another round of organized rainfall and
high mountain snow for the Gulf Coast region, and given the
potential for strong onshore flow, patchy areas of heavy rain are
possible. Farther to the north, partly cloudy skies with some
afternoon showers are likely for the end of the week, although
many of these areas should remain dry.
D. 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 precipitation across portions of southern mainland Alaska,
Thu-Fri, May 7-8.
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