Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1114 AM EST Tue Nov 27 2018

Valid Nov 27/1200 UTC thru Dec 01/0000 UTC

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

12Z Model Evaluation...with Preliminary Preference
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...Overall Pattern Across the CONUS...
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Preference: Blend of 12Z GFS / NAM

A cyclone, becoming stacked, will lumber into the North Atlantic.
The upstream flow pattern over the CONUS briefly goes through a
lower amplitude zonal flow phase, but with an energetic upper jet
leaning from the Pacific into the Southwest states by Day 2. This
jet will support two strong shortwave troughs, one that ejects
toward the southern Plains by the end of Day 3, 00Z December 1st,
and another that approaches the CA/OR coastline at that same time.

The large and stacked cyclone should be well handled by the
models, and consensus suggests the 00Z ECMWF is too far north over
time. Within the more zonal regime the 00Z UKMET emerged as
somewhat an outlier in producing a deeper system and a closed
surface low track from the Tennessee Valley to the mid Atlantic.
Ensemble means have been fairly steady from run to run, whereas
the UKMET has not been. The preference would seem to be GFS, NAM,
ECMWF, but then the ECMWF strays from consensus on Day 3 with
warmer heights over the Great Lakes, perhaps owing to its more
progressive handling of the cyclone off the Northeast U.S. coast.
This leads WPC to prefer the GFS and NAM, noting that the GFS has
been quite steady the past few cycles through Day 3, and the
relatively narrow spread in the ensembles speaks to somewhat
greater confidence / predictability, at least on the large scale.

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

Burke