Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1144 AM EST Wed Jan 2 2019

Valid Jan 2/1200 UTC thru Jan 6/0000 UTC

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

12Z Initial Model Evaluation...with Preferences and Confidence
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...Overall pattern across the CONUS...
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Preference: General model blend through 48 hours, then
UKMET/ECMWF/CMC/GEFS mean blend through Saturday morning
Confidence: Slightly above average

The short range forecast period will be represented with distinct
northern and southern stream flow aloft. There is good model
agreement regarding the northern stream shortwave and associated
offshore surface low near the Northeast U.S. Wednesday night and
into Thursday morning, with the 00Z UKMET slightly more amplified
with the 500mb trough.  A general model blend should suffice for
this region.

The main storm system affecting the continental U.S. through the
end of the week will be a pronounced closed low tracking across
Texas on Thursday and then across the Deep South on Friday, with
an occluded surface low associated with it.  The 12Z NAM becomes
faster with the upper low by 12Z Friday and northeast of the model
consensus, and the 00Z ECMWF indicating a stronger low with
support from its 00Z EC mean.  The 12Z GFS is faster than the
CMC/ECMWF/EC mean by 12Z Saturday, but it has support from the 00Z
UKMET.  A non-NAM consensus is recommended beyond Friday morning.

Across the western U.S., an eastern Pacific shortwave is forecast
to reach the Pacific Northwest Friday morning with the 00Z UKMET
to the south of the model consensus with the surface low.  The 00Z
CMC is slower to the remaining deterministic consensus compared to
earlier runs and there is relatively good ensemble clustering. 
The second and more impactful shortwave approaches the California
coast by the end of the forecast period Saturday morning, with the
ensembles showing better agreement on timing of this feature, but
more spread is noted regarding amplitude.  The GFS is slightly
ahead of the other guidance and the ECMWF slower, with the GEFS
mean and 00Z UKMET being a suitable compromise.

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

Hamrick