Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
153 PM EST Mon Dec 24 2018

Valid Dec 24/1200 UTC thru Dec 28/0000 UTC

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

12z Model Evaluation...with Final Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 12z FV3/12z ECMWF/12z CMC blend
Confidence: Slightly Below Average

The 12z NAM/GFS are close to the consensus with the strong short
wave energy coming ashore over northwest CA after 25/00z, and
remain close as the short wave energy evolves into a long wave
trough over the Four Corners region at 26/12z. After this time,
the 12z NAM becomes faster and stronger with short wave energy
rotating around a developing closed mid level low over the
Northern and Central Plains toward 28/00z. The faster and deeper
short wave energy translates into a faster and deeper surface low
over western WI by 28/00z (as the NAM appears to be exhibiting its
bias to bring surface lows too far into the cold air).

The 12z GFS is also faster than the consensus with the short wave
energy rotating around the closed mid level low toward 28/00z (as
it has been for the past 3 cycles), but it is not as deep as the
12z NAM. Consequently, its surface low is faster that the
consensus, but not nearly as much as the 12z NAM (and its position
is supported by the 12z GEFS mean). The 12z ECMWF/00z ECMWF
ensemble mean are slower with the evolution of the closed mid
level low, and the short wave energy that rotates around it. This
results in surface low pressure over western IA, which is close to
the 12z FV3 position. The 12z CMC was a bit further northeast with
the place of its surface low (between the 12Z ECMWF/12z NAM), so
it was retained in the preferred blend.

Based on the above, a blend of 12z FV3/12z ECMWF/12z CMC is the
preferred blend with the system that affects the Southern Plains
into the Upper MS Valley. At this point, confidence in the
placement of the surface low by 28/00z has dropped, as the model
spread has increased with this feature.

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

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