Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
652 PM EST Mon Nov 18 2019
Valid 12Z Fri Nov 22 2019 - 12Z Tue Nov 26 2019
The forecast period begins on Friday with a large low pressure
system centered over the western half of Alaska, and weakening
going into the weekend with a fast moving low crossing the
northern Gulf of Alaska through Saturday. The models and ensemble
means appear to resolve this initial pattern well with some timing
differences of individual shortwave perturbations pivoting around
the main low, so a majority blend of the latest 12Z models
(GFS/ECMWF/UKMET) was used which maintains good WPC continuity.
This pattern will favor a rather unsettled period across the
southern third of the state featuring heavy precipitation, along
with high winds/waves for coastal regions, including the southeast
Panhandle region.
By Monday, a storm system begins gathering strength across the
north-central Pacific and eventually enters the Gulf of Alaska by
early next Tuesday. Models continue to struggle both with timing
and intensity of this system with the 12Z GFS much stronger and a
bit slower, while the ECMWF is notably weaker. The 12Z CMC is much
farther south and displaced from the ensemble means, so the CMC
was not favored. By the end of the forecast period next Tuesday,
there is a broad model signal for a potentially powerful storm
system emerging from eastern Russia and entering the Bering Sea.
Given how far out in time this event is, the deterministic models
show significant differences with timing and intensity of this
low. Similar to the Gulf low, the ECMWF is weaker than the GFS,
and the CMC is much stronger and farther north. For both of the
systems discussed, a blend of the ensemble means (12z GEFS and 00z
ECENS) was used for days 7-8. The ECMWF also made up a small
portion of the blend for days 7-8 to add a bit of definition given
that it was the deterministic model that most closely resembled
the mean pattern.
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
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