Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1202 AM EST Sat Dec 29 2018

Valid Dec 29/0000 UTC thru Jan 01/1200 UTC

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

00Z NAM/GFS Evaluation...with Preliminary Preferences and
Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 00Z NAM, 00Z GFS and 12Z ECMWF blend
Confidence: Average

Through Tuesday morning, the upper level flow pattern across the
CONUS is expected to feature ridging across both the West Coast
and southeastern U.S. coast with longwave troughing across the
Rockies through the Upper Midwest. Two main features will move
through the U.S. with the first starting off as a closed low over
northwestern Mexico Saturday night which will eject out into the
southern Plains with a negative tilt and a related surface low to
track from near eastern TX to and across the Ohio Valley Sunday
night into Monday. The second significant feature will cross the
Pacific Northwest Saturday night and split into two parts with one
moving to the north-central U.S. and the other amplifying down
through the Intermountain West. 

With the first system, a blend of the 00Z NAM, 00z GFS and 12Z
ECMWF is near the better deterministic and ensemble consensus of
solutions  through Monday. The 12Z UKMET and 12Z CMC differ from
the consensus with the UKMET slower and more west with the track
of the shortwave lifting out across the Mid-Mississippi Valley
while the CMC is displaced with the 850 mb low.

Outside of the faster 12Z CMC, the 00Z NAM/GFS and 12Z ECMWF/UKMET
are in relative good agreement but some amplitude differences with
a NAM/GFS/ECMWF blend nearest to the middle of the ensemble
differences.

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

Otto