Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Aug 28 2018

Valid Aug 28/1200 UTC thru Sep 01/0000 UTC

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

12Z Model Evaluation with Preference and Confidence
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...Overall Synoptic Pattern across the CONUS...
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Preference: Blend of the 12Z NAM/ECMWF/Canadian
Confidence: Average

A medium wavelength trough across the Midwest will eject northeast
into Friday,
trailing a cold front into the Southeast. The next medium
wavelength trough will
rotate around the North Pacific high and approach the West Coast
late Friday.

Models are in generally good agreement into Friday. Subtle
differences in
wave amplitude across the East lead to minimal positional or
intensity
differences at the surface. Any of the operational models can be
recommended
across the CONUS through 31/12Z. Model differences then develop
with the trough
digging into the West on Friday. The NCEP guidance appears
systematically flatter
with this wave compared to non-NCEP guidance. Based on the ridge
position and
highly amplified flow over the Pacific we would expect a bit more
amplitude. But
the 12Z non-NCEP guidance did trend toward lesser amplification
than previous
runs had been showing. The trend brings the NAM back into play for
our preferred
blend on Day 3, whereas the GFS is still the weakest and flattest
of the
operational options for this system. Thus we maintain a consensus
that is centered
on the more amplified ECMWF, Canadian models, but now including
the 12Z NAM as a
viable option.

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

Weiss/Burke