Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1211 AM EDT Tue Aug 27 2019

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

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

00Z Model Evaluation with Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: General model blend
Exceptions: Remove 12z CMC in northern stream after 29/18z
TD 06L NHC Proxy: 12z ECMWF/UKMET blend
Confidence: Above average through 48hrs, average thereafter


Deterministic guidance, including the 00z NAM and GFS, continue to
show very good model agreement with the ensemble suite with
respect to the Southwest US Ridge and deep/stacked cyclone over
Ontario, and the frontal system pressing across the Great Lakes,
Ohio and Tennessee Valleys by early Wed, and into the East Coast
by Thursday; enough to support a general model blend for these
systems through 48-54hrs.  The main uncertainty is the
strength/interaction of deep moisture with TD 06L, which shows a
fairly sizable model spread, particularly in QPF.  The mass fields
relative to the 03z NHC forecast is a blend of the UKMET and
ECMWF.  However, both the 00z NAM/GFS suggest a
shift/redevelopment of this highly vertically sheared system
toward the frontal zone, tightening the gradient/moisture flux
across Southeast New England.  The NAM is more aggressive with the
moisture return, relative to the GFS, which is a little bit slower
to return.  Still, given NHC forecast, a blend of the UKMET/ECMWF
is preferred.

The secondary shortwave in the northern stream starting to
undercut the closed low in SW Hudson Bay, continues to show some
timing issues, especially as it enters the Upper Great Lakes and
the cold front moves into the Upper Midwest.  The UKMET continues
its fast progress, but the NAM has slowed to match the CMC/ECMWF,
and the 00z GFS has taken up the typical fast bias mantle with the
UKMET.  This is a more traditional timing spread in the
deterministic guidance and so a general blend is
preferred...speeding up the NAM/ECMWF/CMC and slowing the
GFS/UKMET, confidence is average for this wave.  Though the 12z
CMC is removed from the preference after 29/18z, when Arctic
stream shortwave energy is drawn south across the Canadian
Prairies into the Red River Valley by early Friday. 

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

Gallina