Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
551 PM EDT Mon Sep 14 2020
Valid 12Z Fri Sep 18 2020 - 12Z Tue Sep 22 2020
...Overview and Guidance/Predictability Assessment...
Upper troughing will linger along 160-170W into next week,
favoring a progressive yet rather vigorous pattern. Lead system on
Friday will lift northeastward on strong southwesterly flow into
Canada. Models still waver on evolution into southwestern areas on
Thursday, but a deterministic consensus blend sufficed among the
12Z GFS/ECMWF/Canadian/UKMET. Next system should dive through the
Bering, across the Aleutians, and find its way to the Gulf late
Sat into Sun. Maintained a deterministic preference of the
GFS/ECMWF/Canadian as the ensembles still lose this system due to
the spread and weak pressure gradient. Finally, last system out of
the NW Pacific showed rather good agreement for the lead time
between the 12Z GFS/ECMWF/Canadian and 00Z ECMWF ensemble mean
(12Z GEFS mean continued to favor another system farther south).
Trend has been deeper with this system and by next Tue (day 8) all
the guidance points to a well-defined wrapped-up system southwest
of Kodiak. Did increase ensemble weighting to tone down the deeper
deterministic solutions as agreement at day 8 does not mean as
much as shorter lead times. To the north, consensus approach
sufficed with weaker troughing through the period in between
anomaly centers. Discounted any model with seemingly spuriously
defined features.
...Weather/Threats Highlights...
Showery patter in the wake of the first system for the weekend
across southern coastal areas, but some enhancement may be
possible. More focused rainfall may return with the third system
next Sun-Tue over the Aleutians to the AKPEN by the end of the
period. Max temperatures will be near to above normal over the
Interior but generally near to below normal over southern coastal
areas into the Panhandle as well as for the North Slope.
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 precipitation across portions of mainland Alaska, Thu-Fri,
Sep 17-Sep 18.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Thu-Sat, Sep 17-Sep 19.
- Heavy rain across portions of the Alaska Panhandle, Sat-Sun, Sep
19-Sep 20.
- High winds across portions of southern coastal Alaska, Thu-Fri,
Sep 17-Sep 18.
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