Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
336 PM EDT Fri Sep 27 2019
Valid 12Z Tue Oct 01 2019 - 12Z Sat Oct 05 2019
Amplified yet progressive upper pattern will trend toward renewed
troughing in the Gulf of Alaska by next weekend. While the
longwave pattern remains generally predictable, the
northern/southern stream interaction/orientation has resulted in
some mixed deterministic model signals. Overall a blend of the 00Z
ECMWF with the 06Z GEFS mean and 00Z ECMWF ensemble mean offered a
good starting point through the period. Recent GFS runs were not
necessarily outside the spread, but were just not preferred based
on the better agreement of the ECMWF to the ensemble means.
Lead system of interest will be in the Gulf on Tuesday with
locally heavy rain and mountain snow for Southcentral coastal
areas into the Panhandle. Next system will lift out of the central
North Pacific toward the eastern Aleutians before turning eastward
into the southern Gulf. 00Z ECMWF nicely split the difference
between the farther north Canadian and south GFSs Thu-Fri. At the
end of the week, uncertainty increases west of the Dateline with a
possible northern stream system diving southeastward into the
Gulf, but did not fully embrace the 00Z ECMWF as it showed
southern stream development in previous cycles though resulting in
a similar forecast by next Saturday. With the likely extratropical
transition of current TD 19W (forecast to be a typhoon as it
recurves through Japan) adding addition uncertainty into the
picture, ensemble mean consensus seemed prudent. This yielded
reloaded troughing into the Gulf downstream of building Bering
ridging.
Fracasso
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 mainland
Alaska, Mon-Tue, Sep 30-Oct 1.
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