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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 1939Z Mar 24, 2019)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
339 PM EDT Sun Mar 24 2019

Valid 12Z Thu Mar 28 2019 - 12Z Mon Apr 01 2019

Over the mainland and vicinity there is still a lot of spread
among individual models and ensemble members for what will happen
to shortwave energy that should cross the mainland late this week
behind an upper high that continues its southeastward path beyond
the Panhandle, and then for the upper ridge/high that builds
behind this shortwave.  On the positive side there is somewhat
more clustering in principle than yesterday--so forecast
confidence is a bit higher than yesterday's minimal level but
remains in the lower half of the spectrum.

The most common theme in today's guidance is that the shortwave
initially approaching the mainland should end up being faster and
less amplified than depicted in the 00Z ECMWF.  During the first
part of the forecast the ECMWF mean has a more subdued reflection
of this idea but then steadily trends closer to the other ensemble
means which have been showing stronger ridging aloft over the
mainland.  By Sun the 00Z ECMWF mean trend reflects a
southeastward adjustment of the upper high from over/north of the
Bering Strait into the mainland.  Interestingly this is back to
what the ECMWF mean was advertising three cycles ago in the 12Z/22
run.  Also of note, 24-hour adjustments in ECMWF/CMC-based model
and ensemble guidance have backed off from their idea of
east-central Pacific low pressure and moisture making their way
into the northeastern Pacific/Gulf of Alaska.  D+5 through D+8
multi-day means have been showing a strong core of positive height
anomalies shifting from the southern coast near the Kenai
Peninsula to along the western coast of the mainland. 
Teleconnections support the latest non-ECMWF consensus of fairly
high heights over the mainland along with an upper weakness to the
south likely not reaching much farther north than 50N latitude. 
Among remaining guidance, the 06-12Z GFS are somewhat slower than
the 00Z GFS/UKMET/CMC and 06Z FV3 GFS with the shortwave of
interest but within the realm of possibility.  Another positive
trend is that latest GFS runs have really dampened out an upstream
shortwave which earlier runs had brought to the mainland by Fri. 
This feature was not well supported by most other solutions.

Over the North Pacific/Aleutians/Bering Sea, there is general
consensus that strong flow ahead of a mean upper low centered near
Kamchatka should propel multiple western Pacific frontal systems
into the western half of the Aleutians/Bering Sea from late this
week into the weekend.  Each front (possibly anchored by or
including a better defined low than in manual progs) may be
accompanied by fairly strong winds.  Between the weekend and early
next week guidance suggests that east-west oriented troughing
aloft will expand across most of the North Pacific with one or
more low centers tracking south of the Aleutians.  A blend
weighted 2/3 toward operational models early and more toward the
ensemble means mid-late period represents consensus well while
accounting for the wide spread of individual models/ensemble
members for individual surface low centers.

Based on preferences over the mainland and vicinity, today's
forecast blend used 30-35 percent of the 00Z ECMWF mean as the
only ECMWF-based guidance.  Operational model components included
the 12Z GFS/06Z FV3 GFS along with the 00Z CMC (into day 7 Sun)
and 00Z UKMET (into day 5), while the 06Z GEFS/00Z NAEFS means
contributed input from about mid-period onward.  Ensemble means
comprised 70-80 percent of the blend by days 7-8 Sun-Mon. 

Rausch


Bullet points from the WPC Days 3-7 Hazards chart can be found at:
https://www.wpc.ncep.noaa.gov/threats/threats.php



WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:

https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html