Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
122 AM EDT Wed Sep 19 2018

Valid Sep 19/0000 UTC thru Sep 22/1200 UTC

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

00Z NAM/GFS Evaluation...with preliminary preferences
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...Overall preference for the entire CONUS...
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Preference: Blend of the 00Z GFS, 12Z ECMWF, 12Z UKMET
Confidence: Average

The biggest difference across the lower 48 through Saturday
involves the track of a mid-upper level trough from the western
U.S. into the north-central U.S. for Thursday and Friday. Out
ahead of this trough, low pressure will organize along a front and
track through the Great Lakes region and eventually into Ontario
for Friday morning. The 00Z NAM trended slower since yesterday and
is now on the slow side of the guidance. the ensemble means have
been consistent in the middle and are best represented by a 00Z
GFS, 12Z ECMWF, 12Z UKMET blend. This blend also applies down
across the southern Plains with an 850-700 mb low/trough.

Some timing differences appear with a second mid-upper level
trough near the Pacific Northwest by Friday into Saturday with the
00Z NAM flatter and more progressive. Again, the ensemble means
show good agreement away from the NAM and are better supported by
a blend of the 00Z GFS, 12Z ECMWF and 12Z UKMET.

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

Otto