Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1140 AM EST Sun Nov 18 2018

Valid Nov 18/1200 UTC thru Nov 22/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of 12Z NAM, GFS and 00Z ECMWF
Confidence: Slightly above average

Over the next few days in the CONUS, the NAM, GFS and ECMWF
provide a fairly well clustered set of forecasts with heights
aloft well within ensemble spread and very close to ensemble
means.

There are some detail differences that do make an impact. For
example, in the Northeast, there is some spread between how far
inland to track a surface low on Tuesday. The trend over the past
several model cycles has been further northwest with the low
position (and higher heights aloft), toward the NAM. Therefore,
greater weight was given to the NAM and GFS in that case.

Along the West Coast, the NAM, GFS and ECMWF all show similar
timing of an approaching trough on Wednesday. However, the trend
for a deeper trough on the past several model cycles has been
toward the ECMWF in this case and more weight was given to the
ECMWF.

Therefore, despite an overall blend of those three models,
slightly different weights were applied in individual cases. The
00Z UKMET and 00Z CMC were excluded from the preference. They show
a trough position off the West Coast that is represented by almost
no NAEFS or ECMWF ensemble members, and are also on the fringes of
the range of model 500mb height spread in the southern stream
through the Southwest and into the Southern Plains. Given more
ensemble support, the preference was to lean toward the NAM, GFS
and ECMWF in general.


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

Lamers