Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Sun Apr 15 2018

Valid 12Z Thu Apr 19 2018 - 12Z Mon Apr 23 2018

Pattern remains fairly well predictable over the medium range for
Alaska. The ensembles were in good agreement through the period
with the largest difference over northern Alaska and then into the
Bering with an initial and secondary system Fri/Sat and then next
Sun/Mon, respectively. This will maintain a rather wet pattern for
coastal areas of south central Alaska into the Panhandle under
southwest flow aloft.

To the north, models and ensembles have wavered a lot on how much
troughing to bring southwestward out of far NW Canada (Banks
Island) to the south of the retreating/meandering upper high.
Consensus seems to be something in between nothing (keeping it
entirely in Canada) and everything (moving a well-defined closed
low across the North Slope) which is where the ensemble means have
been. ECMWF remains more insistent than the GFS to bring at least
some height falls southwestward as do most ensembles. Prefer that
route again today rather than leave the upper low to linger in
Canada with no affect into northern/northeastern Alaska.

South of 60N, system approaching the Aleutians late Friday into
Saturday shows good agreement until about 170W when the 12Z GFS
appeared too far north (north of the islands) while the ensembles
(at least the GEFS/ECMWF ensembles) were clustered just south of
the chain (as was continuity). Preferred something like the older
GFS runs (06Z/00Z) and 00Z ECMWF as it continued eastward into the
Gulf by next Sun/Mon.

Next system will slide into the western Bering Sea late next
weekend but there were large E-W timing differences. ECMWF
ensembles were more consistent and opted to rely on the better
agreeable 00Z GEFS with the 00Z GFS/ECMWF for some added details.


Fracasso