Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Wed Aug 15 2018

Valid Aug 15/0000 UTC thru Aug 18/1200 UTC

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

00Z model evaluation including final preferences
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...Overall Synoptic Pattern across the CONUS...
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Preference: 00Z ECMWF / 12Z ECMWF blend
            00Z UKMET/CMC - secondary option
Confidence: Average

The greatest uncertainty lies across the northern Plains to the
Ohio Valley concerning the evolution of a weakening closed low
currently over the middle Missouri Valley and an upstream
shortwave over southeast Montana. These two features will track
generally toward the east with longwave troughing setting up over
the eastern third of the nation by Saturday morning.

At the surface, a low will track from Kansas/Missouri toward
Chicago Thursday morning and southern Ontario Friday morning. 
GEFS/ECMWF/CMC ensemble low plots show decent agreement as do the
ensemble means, but the deterministic models are on either side of
the good ensemble agreement and have had poor run to run
consistency which lowers confidence from previous thinking. The
00Z GFS is slower/west with the low track, while the 12Z ECMWF and
00Z NAM are a bit east/faster. The 00Z ECMWF adjusted slower with
the upper trough and surface low over the Northeast, but now lies
on the far western or northwestern side of the model spread. The
00Z UKMET/CMC trended toward the ensemble means and actually fit a
decent middle ground with the larger scale synoptic flow but
differ with one another regarding the surface-850 mb low positions
and frontal placement across the Plains. The preference is a blend
led by the 00Z ECMWF and 12Z ECMWF, with neither model showing
ideal given timing differences and a 00Z UKMET/CMC blend a
secondary option.

Elsewhere, model agreement is reasonably good for mass fields,
with the exception of the stronger mid-level trough seen in the
00Z CMC along the West Coast on Friday, though the CMC has been
trending closer to the remaining model consensus and may be used
as part of a blend.

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

Otto