Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1119 AM EST Sun Dec 30 2018

Valid Dec 30/1200 UTC thru Jan 03/0000 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: General model blend through 01.00z, then GFS/ECMWF
blend (non-CMC/non-UKMET)
Confidence: Average

Through Wednesday night, the mid/upper level pattern is expected
to feature ridging off the Florida coast and western US while
pieces of energy associated with a closed low over the southwest
US lift through the central US into the Upper Midwest. Toward the
end of the forecast period, an active northern stream piece of
energy will attempt to phase with the southern stream shortwave,
which introduces more forecast uncertainty, especially day 3
onward.

The first significant system occurs early in the forecast period
as a lobe of mid/upper level energy lifts through the southern
Plains tonight into the Upper Midwest by Monday night. A surface
low will draw up Gulf moisture, resulting in a swath of locally
heavy rain. Here, the early 12z guidance along with the rest of
the 00z/06z guidance shows good model agreement and consistency in
the placement of significant features and QPF. A general model
blend for the first 24-36 hours would suffice.

Beyond that time period, model differences increase as another
northern stream shortwave drops through the northern Plains. How
much of that energy phases with the lingering closed low over the
southwest US remains in question. The 00z CMC/UKMET phased more
compared to the 12z GFS, 00z ECMWF, which causes it to be faster
and a bit more amplified/deeper compared to the model consensus.
The 00z CMC is also considerably faster to eject the energy out
into the Plains. Given the ridging setup downstream, a slower
solution seems more likely. As a result, preference is for a
non-CMC, non-UKMET blend (weighted toward the ECMWF/ECENS) for the
latter portions of the period (01.00z through 03.00z).


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

Taylor