Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
134 PM EST Sun Dec 23 2018

Valid Dec 23/1200 UTC thru Dec 27/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z GFS/GEFS mean, 12Z ECMWF/00Z ECENS
Confidence: Slightly above average

The CONUS flow pattern will generally be rather flat over the next
couple of days as a series of shortwave troughs traverse the
Plains, Midwest and the Eastern U.S. going through Christmas Day.
The guidance is in good agreement with the details of these
shortwaves. Mass field differences begin to arise across the CONUS
by Wednesday though as the large scale flow pattern amplifies in
response to a strong digging shortwave and closed low evolution
over the Southwest U.S. Stream separation will allow for a
southern stream closed low that then ejects east toward the
southern High Plains by late Wednesday along with a developing
area of low pressure. The 12Z NAM becomes the fastest solution to
eject the height falls off to the east. The 12Z ECMWF is the
slowest solution and is actually even a little slower than its own
ensemble mean. Meanwhile, the 12Z GFS, 12Z UKMET and 12Z CMC all
split the difference, but the GFS is on the faster side of the
guidance and has good run to run continuity and also support from
the 06Z GEFS mean.

Elsewhere across the CONUS, there will be additional northern
stream shortwaves arriving across the Pacific Northwest and the
northern Plains. The NAM overall appears a bit too deep with the
energy arriving across the Pacific Northwest on Wednesday, with
the global models led by the GFS and ECMWF showing better
clustering.

Overall, the mass field preference across the CONUS will be a
blend of the GFS, ECMWF and their respective ensemble means.
Confidence is slightly above average given the good ensemble
clustering.


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

Orrison