Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1046 AM EST Wed Dec 26 2018

Valid Dec 26/1200 UTC thru Dec 30/0000 UTC

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

12z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend (non-NAM Fri-Sat)
Confidence: Slightly above average

Longwave troughing with a slight negative tilt at the base will
lift northeast today from the Southwest US into the central Plains
and Upper Midwest. Broad area of upper level divergence combined
with southerly flow in the low levels will promote the development
of widespread precipitation across much of the Plains through the
next 24-36 hours. A surface low is expected to deepen as it tracks
toward Wisconsin later today and tonight. Locally heavy rainfall
will be possible across the southern Plains while heavy snow is
expected across the central/northern Plains.

In general, the 00z guidance and the early 12z guidance shows good
model agreement with respect to the mass fields through 36-48
hours. The UKMET surface low is a bit too fast and to the east
compared to the rest of the guidance, while the 12z NAM is a tad
faster compared to the 06z GFS, 00z ECMWF, 00z CMC. But overall,
clustering is good and a general model blend would suffice.

As the storm system evolves and moves into the eastern US, there
are more differences with respect to the QPF fields. The NAM is by
far the fastest spreading precipitation into New England as early
as Thursday night, while the GFS/ECMWF/CMC/UKMET hold
precipitation back until Friday late morning or even afternoon. So
while a general model blend would probably negate some of the
model biases, the NAM is probably still too fast compared to some
of the other ensemble guidance. As such, a general model blend is
preferred with less weight toward the NAM from hours 48-84.

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

Taylor