Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Mon Aug 26 2019
Valid 12Z Fri Aug 30 2019 - 12Z Tue Sep 03 2019
A robust system will push across the Aleutians and through the
eastern Bering Sea late Saturday into early next week as upper
ridging over the eastern mainland slips eastward into Canada. The
models had wavered on if this potential system would actually come
together, and while there remains notable spread in the ensembles,
the ensemble trend and recent deterministic runs warranted
re-introducing a deeper system into the forecast. However, did not
indicate a strength much below the ensemble means and weaker
deterministic models around 990mb rather than the 970s mb per some
guidance.
Lead weaker system will move across the AKPen and dissipate Friday
ahead of the deeper system. To the north, models still disagree on
how to rotate a shortwave around the main arctic upper low near
the Queen Elizabeth Islands--either westward toward Wrangel
Island, eastward along the coast, or just meander north of the
Bering Strait. Regardless, lead upper low will overtake that
smaller feature if in its way, only to then be overtaken by the
larger system on its heels. Blend between the 12Z GFS and 00Z
Canadian/ECMWF offered a good starting point, then trending toward
the more western and weaker Canadian by next Sun/Mon along with a
majority ensemble weighting (06Z GEFS/00Z ECMWF ensemble mean)
before then just relying on the ensemble means as their agreement
was better than average out to next Tuesday. This would take the
system northward along the western coast as the front slows into
the Gulf. This could set up quite a wet pattern for portions of
Southcentral in favored non-sheltered areas (southern
AKPen/Kodiak/Kenai into PWS). Several inches of rain may be
possible over several days as the system moves through.
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
- Heavy rain across portions of southern Alaska, Sun-Mon, Sep
1-Sep 2.
- Heavy rain across the central Aleutians, Sat, Aug 31.
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