Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Sun Mar 11 2018

Valid 12Z Thu Mar 15 2018 - 12Z Mon Mar 19 2018

For the medium range, upper low initially near the northeastern
Russia Arctic coast will retreat westward as another one rotates
around its west/southwest side to become the next dominant upper
low over Kamchatka next weekend. The flow to its east will feature
the eventual weakening of upper ridging nosing into the Gulf of
Alaska as a lead sfc system and trailing Bering system move
eastward into the Gulf. Finally another system associated with the
new upper low over Kamchatka next weekend will move quickly into
the western Bering Sea and eventually into the Gulf next Monday.
The trend toward more progressive flow has been tough to handle
for the models, but the latest GFS/ECMWF seem to offer good enough
clustering with their reasonably agreeable ensemble means to use
as a starting point. However, there remains considerable spread
along and west of the Dateline regarding where systems may curve
northward or north-northeastward -- ECMWF was farther west and
deeper while the GFS was flatter and farther east. Predictability
horizon of these systems in recent model cycles seems to be about
120hrs or less as the responsible shortwave was well upstream over
Asia or the Arctic where initialization is often poor. Thus, a
trend toward the ensemble means was used to round out the forecast
next Sun/Mon -- 06Z GEFS mean and 00Z ECMWF ensemble mean. The
GEFS has really struggled with the flow over most of North America
in recent runs but at least its 06Z run was more in line with the
ECMWF ensemble mean, which has shown better consistency.


Fracasso