Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
349 PM EDT Fri Apr 13 2018

Valid 12Z Tue Apr 17 2018 - 12Z Sat Apr 21 2018

An upper low is forecast to move out of the Bering Sea toward the
AKPen as another one initially over Banks Island in NW Canada may
charge westward across the North Slope. The former has much better
predictability than the latter, and the ensembles have grown apart
over northern areas vs southern areas.

To areas south of 65N, a multi-model blend sufficed to start the
period as the models have been steady in strength/track of the
Bering low with triple point redevelopment near Kodiak on
Wednesday and its eventual landfall into the Panhandle next
Friday. A trailing system is still on track to lift northeastward
out of the central North Pacific toward the central Aleutians by
the end of the week into next weekend per the ensembles and even
the deterministic GFS/ECMWF/Canadian.

To the north, ensembles have trended apart with the ECMWF
ensembles most emphatic on bringing an upper low bodily westward
across the North Slope to the Bering Strait on Thursday while its
ensemble mean was weaker and a bit slower. The GFS/Canadian and
nearly all of their ensembles keep most of the upper low confined
to NW Canada but the 12Z GFS did allow a portion to slide westward
behind the 00Z ECMWF. Opted to blend these inputs with a
preference toward the 00Z ECMWF ensemble mean and 12Z GFS which at
least allow some form of an upper low (though not explicitly
drawn) to slide westward. This may help elongate the in situ
Bering low along 55N from the western waters to the Gulf.
Confidence is low in the details and it may take a few more cycles
for the ensembles to form a consensus as the source region for
this upper low lies over northern Siberia in a typically poorly
sampled area (even by satellites).


Fracasso