Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
230 PM EST Thu Nov 29 2018

Valid 12Z Mon Dec 03 2018 - 12Z Fri Dec 07 2018

...Guidance/Predictability Assessment...

Latest GFS/ECMWF and GEFS/NAEFS/ECMWF ensembles seem to be
reasonably clustered with the synoptic scale pattern evolution
next week, but growing smaller scale embedded system variance
favors an increase in weightings for ensemble mean components with
time in a favored composite blend solution through next week.

...Pattern Overview and Weather Highlights/Hazards...

The WPC Alaskan medium range period starts Mon/Tue with an
energetic shortwave lifting over western Alaska to the North
Slope/Arctic on the periphery of an interior Alaskan upper ridge,
leading to a swath of modest/moderate snows. This ridge rebuilds
in the wake of shortwave passage to maintain the rest of next
week. An upstream closed upper level low will meanwhile slide just
south of the Aleutians toward the AKpen Mon-Wed, resulting in a
deep surface low. There is a threat of heavy rainfall for
southwest AK (especially for coastal locations) as a lead front
will also be slow to push eastward due to downstream ridging.
Southerly moist flow into southern AK will also fuel widespread
precipitation as enhanced by slow deep surface low appraoch. The
low and precipitation potential weakens/lifts northward to the
eastern Bering Sea/western AK around the rebuilt blocking ridge
centered over the mainland/Southeast AK. However, system genesis
underneath may work into the Gulf of Alaska late next week to
support additional enhanced precipitation potential with renewed
southerly fetch into southern AK.

Schichtel


WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html