Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1103 AM EST Tue Dec 04 2018

Valid Dec 04/1200 UTC thru Dec 08/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: 12z GFS and 00z ECMWF/UKMET blend
Confidence: Above average

Low ensemble model spread continues through this time period
particularly through 07/00z (60hrs), with exception of the
Northwest Atlantic deep cyclone that affects the maritime.  Here,
the 12z NAM continues to be very strong but also left of the
ensemble cluster track, while the 00z UKMET is off the slower side
of the packing especially aloft, leading to greater vertical tilt
than say the ECMWF/GFS or CMC (please see OPC High Seas forecast
for more details).

Behind this exiting wave up the coast, the Northern global vortex
dips into the Great Lakes, with low amplitude fast moving
shortwaves crossing the region through the remainder of the
forecast.  Here, the 00z CMC remains more amplified overall
especially with the late short-term forecast wave in the upper
Midwest, while the NAM/ECMWF are a bit more washed out than the
UKMET/GFS...suggest a non-CMC solution for this region.

The largest spread remains with the amplified trof entering the
Southwest US/Northwest Mexico Friday, spurring height-falls and
moisture flux across the Southern Plains with some potential for
freezing rain across N TX into W OK.  The NAM which had been a
clear outlier with prior runs, has trended faster to orient more
favorably, yet loads the trof in the middle with of the wave
leading to best forcing further north across the Southwest and
further south across TX, this is less favorable within the suite. 
 The 00z CMC depicts a broader trof, away from the overall trend,
which was enhanced by the 00z ECMWF being a bit sharper, slower
and stronger overall, even compared to the 00z ECENS suite, this
should further eliminate the CMC from preference overall;
especially considering the lack of upstream ridging leads to large
spread over the Eastern Pacific with the next large scale trof. 
The 12z GFS, shows some typical bias being a bit faster/flatter
than the ECMWF but with the 00z UKMET in the same
orientation/timing/placement of the wave and forcing convergence
across the Southern Plains...believe a blend of the three will be
quite strong with fairly high confidence given the typical
potential for spread from systems exiting out of Northwest Mexico
(multiple stream interaction from north Pacific/Tropical Pacific
and Western Gulf).

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

Gallina