Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
228 PM EST Tue Jan 23 2018

Valid 12Z Sat Jan 27 2018 - 12Z Wed Jan 31 2018

Model guidance remained in good agreement with the large scale
evolution of flow over Alaska this weekend, which will feature a
deep vortex sliding south into the Gulf of Alaska and an upstream,
highly amplified upper ridge, building in over the Bering Sea. 
Model spread and forecast uncertainty quickly increases by early
next week.  In particular, models are showing a wide range of
solutions with mid-level energy dropping southward down the
eastern edge of the highly amplified ridge Sunday into Monday. 
Recent runs of the ECMWF appear to be aggressive outliers with
amplifying the energy and pinching off an elongated upper low near
the Aleutians, but this solution does have support from some of
the 00Z ECMWF ensemble members.  Regardless, the uncertainty with
this feature is contributing to high uncertainty with the
progression of Pacific systems approaching Alaska towards the
middle of next week.

The WPC Day 4-5 forecast used a blend heavily weighted towards
deterministic guidance in order to account for the decent model
agreement early in the forecast period.  For Day 6-8, the WPC
forecast transitioned to predominantly ensemble means due to the
diverging model solutions early next week.             


Gerhardt