Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1214 PM EDT Fri Jul 27 2018

Valid Jul 27/1200 UTC thru Jul 31/0000 UTC

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

00Z model evaluation...with preferences and confidence
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...Overall Synoptic Pattern across the CONUS...
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Preference: General blend except for central US (12z GFS/00z ECWMF)
Confidence: Average

Guidance continues to be fairly consistent with the forecast over
the next 3 days and depict a strong similarity with the overall
pattern.  The upper low over Southeast Canada will shift away with
a remaining broad positive tilt trof, southwesterly flow regime
back toward the amplifying longer, broader wave across the Lower
MO river valley into the Ozarks by late Monday.  Numerous
northwesterly flow shortwaves, and upscale MCS vort centers will
slide through this weakness from the Central Rockies through
KS/AR, aiding to this longer term trof.  Given the influence of
upscale growth of this MCS centers there is moderate spread,
uncertainty in precise timing/focus along the lingering NW to SE
frontal boundary.  The 12z NAM shows typical bias, of stronger
maintenance of each MCV a bit longer, leading to a slightly
faster/deeper larger scale trof toward the Southeast.  The 12z GFS
remains fairly consistent in the larger scale mass and matches
well with the 00z ECMWF and the mean ensemble suite.   The UKMET
shows some stronger retention of the waves particularly toward Day
3 rotating into the Ohio Valley leading toward a northward shift
(which seems less likely given stronger instability/moisture
return/intersection with the boundary being further south).  The
CMC shows similar mass fields but is much weaker/broader with the
internal waves leading to some departure from ideal, but could be
used in a blend at lower weighting if desired.  

The broad upper level low off the West Coast, shows some timing
and size (breadth of inner core) differences as it evolves into a
closed system by late Mon.  Here the typical orientation/setup
between the guidance is noted;  the UKMET/NAM/GFS are a bit deeper
stronger faster, while the ECMWF/CMC are smaller and slower to
evolve.  Typically splitting the difference verifies well...enough
to support a general model blend for this system (and the deep
closed ridge in the southwest).  

All considered will favor a Blend of the 12z GFS and 00z ECMWF to
account for the central US, but a general model blend will work
out well elsewhere.   Confidence is average in the central US
given the variance related to convective upscale development
(which is chaotic and harder to resolve precisely). 


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

Gallina