Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1247 AM EDT Wed Aug 07 2019

Valid Aug 07/0000 UTC thru Aug 10/1200 UTC

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

00Z Model Evaluation with Final Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend until 12Z Friday
            Non-NAM/GFS blend afterward
Confidence: Average

Model mass fields are in very good agreement through Thursday
Night, with similarly good agreement in the QPF fields for the
same (Days 1-2) time period. Therefore, a broad-based model blend
is preferred through Day 2, which should help account for typical
uncertainties due to convective processes.

After Thursday Night, greater differences begin to emerge,
particularly along the periphery of the upper level ridge that
will be shifting from the West into the Plains. The 00Z NAM and
GFS show a faster progression of a trough into the West Coast than
the 12Z ECMWF, UKMET and CMC do. Ensemble members are clustered
relatively close to their deterministic counterparts, and this is
a fairly common bias (GFS faster). Given the strength of the
downstream ridge and the initial nature of the trough (strong
closed low), a somewhat slower progression is favored.

Across the Canadian Rockies, the 00Z GFS also shows a faster
progression with a trough digging another 10 degrees of longitude
to the east of the model consensus by Saturday morning. This seems
less likely as it would require a trough to quickly push into a
ridge axis, and there is limited ensemble support (even from GEFS
members). Therefore, the preference in the Western U.S. and into
the Northern Plains is for a blend of the ECMWF, UKMET and CMC
after Thursday Night.


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

Lamers