Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Fri Dec 14 2018

Valid Dec 14/1200 UTC thru Dec 18/0000 UTC

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

12Z Model Evaluation...with Final Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: non 12Z CMC blend
Confidence: Average

...19Z update...

Changes in the 12Z ECMWF/UKMET/CMC were relatively minor keeping
the CMC out of the preference but with the 12Z UKMET shifting
enough toward the NAM/GFS/ECMWF consensus both east and west to
include it as part of the overall preference.

...previous discussion follows...

An amplified upper level pattern over the lower 48 will feature
general troughing in the eastern U.S. with a combination of
shortwaves to impact the East Coast. A trio of mid-upper level
waves will impact the western U.S. through Monday, the first of
which will be making landfall today, followed by longwave trough
Sunday night and a third system to near the Pacific Northwest late
Monday.

Out East, ensembles have come into much better agreement compared
to previous days with trends toward a middle ground solution
reasonably represented in the latest deterministic guidance. The
largest difference is with the track of a surface low which
develops off of the northern Mid-Atlantic coast on Sunday. The
position of the surface low is reasonably well clustered in the
ensemble guidance but the 12Z NAM is toward the west side of the
ensemble low plots but within reason, while the 00Z CMC is toward
the far east side of the ensembles. Strength-wise, the 12Z GFS is
likely too weak but a blend of strength/position of the 12Z
NAM/GFS and 00Z ECMWF is preferred overall for the East Coast
through Monday. Also of note is that the 12Z NAM is slower with a
shortwave originating over the West as it reaches Quebec on Monday
compared to the remaining consensus.

Across the western U.S, there is relatively good agreement between
the 12Z NAM/GFS and 00Z ECMWF but the 12Z GFS was slightly faster
than the model consensus on Sunday with a shortwave nearing
Oregon/Washington. The 00Z CMC shows some differences, but here
again, a blend of the 12Z NAM, 12Z GFS and 00Z ECMWF is preferred
and nearest to the ensemble means and consensus.

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

Otto