Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1152 PM EST Sun Dec 30 2018

Valid Dec 31/0000 UTC thru Jan 03/1200 UTC

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

00Z NAM/GFS Evaluation...with Preliminary Preferences and
Confidence
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...Overall pattern across the CONUS...
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Preference: General model blend through 01.12z, then GFS/ECMWF/NAM
blend (non-CMC/non-UKMET)
Confidence: Average

The mid/upper flow pattern across the nation starts off with
ridging off of the Florida coast and western U.S. with mean
troughing in the west-central U.S. Over the next 3 days, a slow
shifting toward the east of features is expected with a slow
moving closed low nearing the Texas panhandle while a number of
shortwaves track through the northern stream.

With the southern stream closed low slowly moving east toward the
Texas Panhandle, the trend in the ensembles from Wednesday into
Thursday has been slower, with an average GEFS/ECMWF ensemble mean
position just ahead of the agreeable 00Z NAM, 00Z GFS and 12Z
ECMWF. While there is certainly room for the 00Z NAM, 00Z GFS and
12Z ECMWF preference to be a little too slow, the 12Z UKMET is
significantly slower and the 12Z CMC is significantly faster
(edges of the ensemble spread).

For the northern stream systems, a blend of the 00Z NAM, 00Z GFS
and 12Z ECMWF is nearest to the ensemble mean position/timing with
the shortwaves tracking near the U.S./Canadian border and offshore
of the Pacific Northwest. Despite some minor differences, this
3-way blend is closer than including the 12Z UKMET or 12Z CMC.
There are larger differences offshore of the Pacific Northwest by
12Z/03 with a cyclone several hundred miles west of
Washington/Oregon but at least through the end of the short range
(12Z/03) a NAM/GFS/ECMWF blend is best for Washington and Oregon..

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

Otto