Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
235 PM EST Tue Mar 06 2018

Valid 12Z Sat Mar 10 2018 - 12Z Wed Mar 14 2018

With respect to the evolution of the long wave pattern across
Alaska, the models are generally in good agreement for much of the
medium range period. The closed cyclone forecast to move across
the mainland this week will anchor an amplifying mean trough over
the eastern Pacific/Gulf of AK during the weekend into early next
week. Ahead of it, upper ridging will build north and westward
into eastern AK.  Upstream, a deepening upper trough over eastern
Russia will help pump up a mean ridge that will slowly progress
across the Aleutians through Day 6.

There is, however, much less agreement handling the individual
short wave features traversing this amplifying flow. The most
prominent difference early in the period is with the handling of a
trough that ejects from eastern Russia Thursday and into the
Bering Sea Day 4 (Saturday).  The ECMWF...as it has for several
recent runs...is notably stronger than other guidance and has the
affect of forcing the downstream upper trough to push into the
western coast of the lower 48 by early next week.  The 00Z GFS and
Canadian are much weaker, and focus stronger cyclogenesis with a
short wave ejecting from the southern polar stream (lifting
northeastward from Japan Friday); the ECMWF does also strengthen
this feature, but it's approximately a day behind the Canadian and
GFS. Looking at the latest 12Z guidance, the models basically
remain consistent with their prior solutions.  Considering the
spread of solutions and the fact that model timing of systems
moving through this amplifying flow is challenging and will very
likely change from run to run, we mostly opted for a compromise
blend of the ECMWF and NAEFS ensemble means with both systems,
though given the better run to run consistency of the ECMWF, did
lean a little in its direction versus the NAEFS.

Late in the period, Days 7-8, believe the Canadian and its
ensemble solutions are breaking down the ridge too quickly over
the Aleutians and western mainland AK as it drives a short wave
across the Aleutians and southern Bering Sea 00Z 3/14.  The ECMWF
and GFS/GEFS look to have a somewhat better handle in this area,
though differ with the forward speed of the short wave. We opted
for a compromise between their respective ensemble means with
respect to the short wave timing and strength.

Elsewhere...the 00Z GFS seems to be out on its own phasing an
Arctic upper low with a short wave lifting northward through
interior AK late Saturday-Sunday.  Other guidance, including the
GFS and ECMWF ensembles either keep them separate or don't resolve
the Arctic feature.  Notably the new 12Z GFS has trended away from
this forecast evolution, so at this time have low confidence in
the 00Z run across this area for Days 4-6.

To sum up the model preferences for this forecast...we went with
mostly a blend of the 00Z ECMWF/GFS deterministic for Day 4 where
there was good agreement.  Days 5-6 were a blend of the ECMWF
ensemble mean and NAEFS, with slightly heavier weight to the ECMWF
ensembles. For Days 7-8, generally favored a ECMWF and GFS
ensemble mean blend.

Klein