Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
244 AM EDT Thu Sep 27 2018

Valid Sep 27/0000 UTC thru Sep 30/1200 UTC

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

00Z Final Model Evaluation...with Preferences and Forecast
Confidence
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...Overall Preference for the Entire CONUS...
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Preference: 00Z GFS/00Z ECMWF/00Z GEFS mean blend
Confidence: Slightly above average

A long wave trough remains the dominant upper level feature over
much of the continental U.S. through Friday morning, before
transitioning to a more zonal flow across the northern tier by
this weekend in response to a building upper ridge over the Gulf
Coast region.  The Rex block pattern over the eastern Pacific on
Thursday breaks down some when the upper low slowly tracks
eastward to the West Coast by Saturday night.  At the surface, a
cold front will track across the plains through the end of the
week with a large surface high settling in across the central and
eastern U.S. by the weekend.

There is relatively good agreement among the deterministic and
ensemble mean guidance through the period with just minor
differences in the 500mb heights with the longwave trough across
the northern tier states.  The 00z NAM is slightly more amplified
across the Great Lakes and Mid-Atlantic region with a weaker ridge
over the Gulf, and the CMC has trended farther south with the
track of the closed low approaching northern California on
Saturday.  The UKMET is faster with a shortwave trough crossing
southern Canada by the end of the forecast period Saturday night. 
Therefore, a blend of the 00Z GFS and 12Z ECMWF should suffice for
most areas through Saturday night.

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

Hamrick