Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1224 AM EDT Sun Apr 15 2018

Valid Apr 15/0000 UTC thru Apr 18/1200 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...

00Z NAM/GFS evaluation with preliminary preferences
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...Midwest Cyclone Becoming Centered Over New England by
Wednesday...
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Preference: Blend of 00z NAM with 12z ECMWF and UKMET

A cyclone over the Midwest states early in the period will not
encounter blocking, per se, but will move only slowly as it skirts
beneath northern stream shortwave ridging, the stacked low
reaching New England on Tue/Wed. The ECMWF has been very
consistent from run to run, but may be a bit too suppressed /
south and east with its solution by Day 3, per its tendencies.
Input from the GEFS, NAM, and UKMET, suggest tugging the low a
little farther north and west of the ECMWF track. It is the GFS
that ends up being more questionable, as it gains latitude so much
more quickly than the other models, and has been more variable
from run to run. Therefore, while the GFS may be useful to some
extent, we prefer a blend of the NAM/UKMET/ECMWF.


...Trough Progressing Through the West, Reaching the Plains late
Tuesday...
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Preference: Blend of 12Z ECMWF/UKMET

A parade of energetic, medium wavelength systems is set up from
the Pacific Ocean toward western and central North America. The
next system will enter the West on Sunday, reaching the
continental divide early Tuesday, and swinging negatively tilted
onto the Plains by Wednesday morning. Late in this process the
southern portion of the trough becomes more distinct, with the
possibility of a small closed mid level circulation forming in the
Central Plains / lee of the Rockies. Throughout the 3-day period
the operational GFS appears too fast, and does not induce its
deepening up through 500 mb early Wednesday despite a favorably
energetic flow emerging from the mountains. The NAM, on the other
hand, may be showing its typical bias by producing a solution that
represents the strong, cold end of the spectrum. The ECMWF and
UKMET were good middle ground solutions with greater ensemble
support.


...Next Pacific Trough Reaching the West Coast Tuesday Night...
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Preference: Blend of 00z NAM/GFS and 12z ECMWF

As the above system pulls into the Plains, the next Pacific trough
will approach the West Coast Tuesday night. As with the other
systems during this period, the ECMWF seems to be handling this
pseudo-progressive, medium wavelength flow very consistently.
Spaghetti plots containing all GEFS, EC, and CMC ensemble members
and with multiple model cycles plotted side by side, show the
other modeling centers' solutions trending in aggregate toward the
ECMWF solution. As of the 00z cycle, the NAM and GFS are similar
enough to the 12z ECMWF to combine these three in a preferred
solution.

Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

Burke