Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Fri Aug 09 2019

Valid Aug 09/0000 UTC thru Aug 12/1200 UTC

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

00Z Final Model Evaluation with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General model blend, with less weight on 00Z NAM
Confidence: Average

07Z Update: 00Z Non-NCEP suite showed little variation from the
12Z. There remains very good consensus in the overall synoptic
pattern, at least through day 2, with the most significant
difference being lowered heights across the central CONUS on the
NAM versus the rest of the guidance. On day 3 /Sunday/ more
spatial discrepancies crop up with respect to interaction between
a shortwave lifting around the periphery of the Monsoon ridge into
the SW, and the dampening of a closed low moving into the northern
Rockies. These features together will eventually create flow
across the CONUS that is more zonal, but exactly how quickly this
occurs varies among the guidance. For continuity, will make no
changes to the preferred blend since it is small scale features on
day 3 which feature the greatest spread, and the overall mass
fields remain in relatively good agreement until then.

Previous Discussion:
Large ridge across the middle of the CONUS will be book-ended by
troughs across the Northeast and the Pacific NW. The global
consensus is generally well aligned with the primary trough axis
swinging through New England while the main upper low remains
displaced into Canada, with the second low diving into northern
California driving downstream ridge amplification across the
Plains. The NAM is several DM cooler with the ridge across the
Plains, and this seems unlikely due to lack of model support plus
the likelihood of ridging to enhance in response to the upstream
trough diving into California. Despite it being weaker with the
ridge, the overall pattern remains similar and has little impact
to QPF until the end of the forecast period, so a minimalist
weight approach seems best. Other than that, a general model blend
should suffice. The GFS is a bit strong with shortwaves lifting
into the Monsoon flow across the SW, especially on day 3, so a
GEFS solution to blend out some of this amplitude may be best, but
even then the overall spread is minimal.

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

Weiss