Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
303 PM EDT Wed Aug 08 2018

Valid Aug 08/1200 UTC thru Aug 12/0000 UTC

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

12Z Model Evaluation and Preferences with Forecast Confidence
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...Overall Synoptic Pattern across the CONUS...
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Preference:     NW CONUS: Non-CMC blend
   Central/Eastern CONUS: Non-NAM blend
   Confidence: Average

The greatest model variance continues to be related to the timing
of the closed low approaching the Pacific Northwest...with the
differences across the Gulf Coast being a fairly close second
place.  The 08/12z GFS continued to be a sharper/deeper solution
when compared the 08/12Z NAM...and the 08/12z ECMWF after 11/12z.
The 08/12z ECMWF maintained fairly good run to run continuity, so
it remained slow with merging/phasing with northern stream energy
at landfall.  As such, it leaves the 08/12z Canadian on the
slow-side of the envelope of solutions by the end of Day 3.  Will
continue to favor a non-CMC blend here.

Overall synoptic to global pattern is well agreed upon with closed
low/amplified ridge/and broad eastern half of the CONUS in the
trof, which is seen well in the last 5 cycles/ensemble trends. 
However, mesoscale to synoptic details show subtle but important
differences, typical of each model bias, and particularly late day
2 into day 3.   The exiting mean Canadian trof that stretches into
the northeast, with associated surface wave in Northeast on
Thursday, an idea that the models agreed upon with respect to
timing although the models either show greater stretching or
greater concentric solutions with the base of the trof through the
Northeast.  The 12z NAM shifted to a solution that was in better
agreement with the consensus of other models and can be included
in any blend here. 

Similarly, the lingering positive tilt trof that starts to
consolidate/amplify across the Lower MS valley Friday is still
most aggressively compact by the 08/12z NAM and ejects
further/faster toward the east.   While, the 08/12z ECWMF and
08/12z GFS are a bit more elongated/stretched through into the Red
River Valley matching well with the overall ensemble trend and
likely evolution given the breadth of diffluent flow across the
Midwest/MS valley, hinting on some weak retrograding across TX
into northern Old Mexico.  The 08/00z GFS does shear the wave
toward the east eventually a bit faster than the ECMWF, but not
significantly so, to blend the two. 

Farther west, the closed low off the west coast will reach the
Pacific Northwest in the Friday/Saturday time frame.  Here the
08/12z UKMET remained very slow and well out of phase with the
remaining guidance.  The 08/12z GFS continued to slightly outpaces
the means, per typical bias but not significantly so, but would
favor something closer to the ECMWF/CMC/NAM.  

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

Bann