Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
200 PM 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...listing Preference and Confidence
***12Z ECMWF Unavailable as of 19Z***
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...Overall Pattern Across the CONUS...
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Preference: Blend of 12Z GFS / NAM
Confidence: Average

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 had emerged as
somewhat an outlier in producing a deeper system and a closed
surface low track from the Tennessee Valley to the mid Atlantic.
The 12Z UKMET dampened this system, and is generally in step with
the NAM/GFS-led consensus for timing and placement of the large
scale features, but is still on the fringe of the ensemble
envelope over the eastern U.S. on Days 2 and 3. Ensemble means
have been fairly steady from run to run, whereas the UKMET has not
been. The 12Z ECMWF was unavailable as of this writing owing to a
data flow issue at NCEP. The WPC preference for the CONUS pattern
is 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