Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1119 AM EST Tue Dec 11 2018

Valid Dec 11/1200 UTC thru Dec 15/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...

Preference: Blend of the 12Z NAM, GFS and 00Z ECMWF
Confidence: Average

Model spread begins to increase markedly after Wednesday Night
(after 13/12Z), with the main differences generally related to
timing. In particular, there are timing differences with the
digging wave that closes off a low aloft in the southern US on
Thursday and Friday. There are also timing differences with the
next wave approaching the Pacific Northwest on Friday.

Timing variability is similar with these waves, with the 00Z CMC
and 12Z GFS generally on the fast end, and the 00Z UKMET and 00Z
ECMWF on the slow end. The trend on the GFS and NAM, particularly
with the southern US low, has been to slow things down. This has
been a consistent trend over multiple model cycles, and now the
GFS and NAM are situated relatively close to the 00Z ECMWF in
terms of the positioning of the cyclone over Texas. Better
agreement with the low over Texas has led today's model preference
to lean toward a blend of the NAM, GFS and ECMWF.

More significant timing differences remain over the Pacific
Northwest, but a consensus between the NAM, GFS and ECMWF is
roughly in the middle of the ensemble distribution and close to an
average of the ECMWF Ensemble Mean and GEFS Mean. The UKMET and
CMC were not included in the preference today as they would be
close to the most extreme model member in several cases. Although
they cannot be totally ruled out, they have far less ensemble
support than the other deterministic models.


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

Lamers