Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Thu Mar 29 2018

Valid 12Z Mon Apr 02 2018 - 12Z Fri Apr 06 2018

During the extended periods a strong high will retrograde over the
Bering Sea, allowing a trough to deepen (likely to contain an
embedded closed low eventually)
over South Alaska and eastern Gulf. Model guidance has started to
converge on the evolution of this feature but still sluggish on
resolving individuals shortwaves within the flow. There is still
meaningful uncertainty in some forecast details at the surface and
aloft.

The latest ensemble means continued the trend of having a stronger
high by the mid/late periods than the deterministic runs.
Initially the preferred blend comprised of about 55% 00Z
CMC/ECWMF/06Z and 12Z GFS and 45% of the ensemble means then
quickly transitioned to a heavy weighting of the ensemble, 85% by
day 8.

A significant question mark by the end of the period is how much
interaction there may be between the mainland into Bering upper
trough/low and energy that may track out of the north-central
Pacific.  While the ensemble means provide the best starting point
for the manual forecast, it is possible that they could be a
little too eager to phase the two streams.  Operational model
signals are mixed regarding how much stream interaction may occur
and when.  This issue will require monitoring over coming days.

Campbell/Rausch