Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1127 AM EST Sun Dec 16 2018

Valid Dec 16/1200 UTC thru Dec 20/0000 UTC

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

12Z 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
Confidence: Slightly Above Average

Model agreement continues to be above average across the lower 48
through Wednesday as the flow pattern evolves toward low-amplitude
longwave ridging along the West Coast and longwave troughing over
the center of the nation. There are some differences worth
mentioning, but non are significant enough to exclude a single
model at this time which translates into a general model blend of
the latest deterministic guidance.

The 12Z NAM is slightly more amplified with a shortwave nearing
the Pacific Northwest late Monday with its main surface low near
Haida Gwaii displaced southward of the remaining model consensus.
However, the affects of these differences into Washington and
Oregon are minimal. There are also some minor timing differences
concerning the translation of a longwave trough into the center of
the nation Tuesday into Wednesday with the 12Z NAM fastest and 00Z
UKMET slowest, but a blend of the relatively minor differences is
near the ensemble means providing a favorable middle ground.

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

Otto