The Weather Prediction Center

Model Diagnostic Discussion

[Abbreviations and acronyms used in this product]
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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
240 PM EDT Mon Aug 20 2018

Valid Aug 20/1200 UTC thru Aug 24/0000 UTC

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

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

...Overall Synoptic Pattern across the CONUS...
Preference: 00Z ECMWF/00Z CMC/12z GFS, except more CMC and GFS for
the northwestern U.S.
Confidence: Slightly above average

The weather pattern across the continental U.S. through the middle
of this week will feature an upper level ridge centered over the
southern plains, and multiple perturbations in the flow across the
northern tier of the nation.  The main feature of interest is the
strong surface low that will track across the Upper Midwest and
then the Great Lakes, accompanied by a large scale trough that
will reach the East Coast by Wednesday.  A second upper level
trough is forecast across much of the northwestern U.S. with a
narrow ridge axis extending into British Columbia.

The models are in decent synoptic scale agreement through this
forecast period with some minor timing and magnitude differences
noted regarding the trough progressions.  By Tuesday afternoon,
the 00Z UKMET is slightly flatter with the upper trough over the
Great Lakes and a little more expansive with the upper ridge over
Texas.  By the end of the forecast period Thursday morning, the
00Z ECMWF is a little ahead of the model consensus with the trough
axis over Montana, and the NAM is slightly slower.  There is
enough agreement among the ECMWF/GFS/CMC to merit a blend of these

Model trends at
500 mb forecasts at


Last Updated: 240 PM EDT Mon Aug 20 2018