Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1259 PM EDT Thu Sep 26 2019

Valid Sep 26/1200 UTC thru Sep 30/0000 UTC

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

12Z Model Evaluation with Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: Non-NAM Blend
Confidence: Slightly above average

Models continue to show excellent agreement overall on a pattern
shift over the CONUS, with a trough digging sharply into the
Northwest on Friday, and continuing to amplify over the weekend. A
related amplification of the downstream ridge over the eastern
half of the CONUS is also projected. Model spread is relatively
limited in most cases. Notable differences, while not large in an
absolute sense, appear to be related to the amplitude of the
trough as it begins to dig into the West on Saturday, and then
timing of a shortwave kicking out into the northern Plains on
Sunday.

The 12Z NAM shows the greatest amount of variation with the
consensus of the global models and ensemble means. In particular,
it digs the trough faster, and shows a quicker ejection of the
shortwave into the Plains. This is not favored given a lack of
ensemble support, and the expectations of slower motion over the
weekend as a large mid-upper level low closes off.

Otherwise, deterministic models are contained well within the
envelope of ensemble spread, and a blend of the remaining global
models (ECMWF, GFS, CMC, UKMET) is preferred to account for
additional minor uncertainties.


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

Lamers