Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1117 AM EST Sat Dec 29 2018

Valid Dec 29/1200 UTC thru Jan 02/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Average

A persistent subtropical ridge over the Caribbean will keep
longwave troughing mainly confined to the central US through
Wednesday while upper level ridging hangs on across the western US
as well. One shortwave trough currently over the central Plains
will race off to the northeast into the Great Lakes region later
today, while another over the southwest US pinches off and becomes
closed through the weekend. By early next week, a stronger
shortwave dropping out of the Pacific Northwest will kick the
closed low northward and begin to phase in as well. This will lead
to surface cyclogenesis and draw Gulf moisture northward into the
mid-MS and lower Ohio Valleys.

Overall, there is above average model agreement with this flow
pattern as seen in the 00z guidance and early look at the 12z data
coming in. The surface low track with the early next week storm
system from TX to MI shows really good agreement with just some
minor speed differences. QPF fields are in good shape, though the
NAM does paint higher QPF with the warm frontal passage across
northern MS/AL and TN Sunday evening. But otherwise, the models
paint similar values as the system lifts northward and then a cold
front sweeps in behind it.

For the northern stream shortwave crossing through Monday evening
into Tuesday, the GFS is a bit faster with the trough swinging
through compared to the ECMWF/CMC. It is also warmer in the
low/mid levels while the ECMWF/CMC are much colder. Phasing with
the southern stream is greater in the ECMWF solution, which yields
higher QPF compared to the GFS and even the NAM. The ECMWF might
be too aggressive with its QPF, so a general model blend will
likely be a good approach at this time.

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

Taylor