Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
256 PM EDT Thu Jul 12 2018

Valid Jul 12/1200 UTC thru Jul 16/0000 UTC

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

12Z Model Evaluation  Final Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Model Analysis for the CONUS...

Overall Preference: 12z NAM/GFS/ECMWF blend
General Confidence: Slightly above average
                    Slightly below average off east coast

19z update: The east coast system continues to elude consensus as
the 12z ECMWF trended slower and stronger and generally matches
the 12z UKMET which while shallower than prior 12z/00z run...is
still deeper than the NAM/GFS and now the CMC which is weakest and
matches closest to the GFS.  The 12z GEFS shows this spread by not
presenting a surface wave...so will trend away from the
ECMWF/UKMET or utilize the old 00z ECMWF over the 12z ECMWF for
this system.

Elsewhere the UKMET remains much faster than the consensus with
respect to the closed low in central Canada and associated frontal
zone in the northern Plains by Sun.  The ECMWF was a bit faster
and even outpaced the GFS...but still well within the realm to
have solid confidence keeping it in a blend with the GFS/NAM
across the CONUS (maybe a bit less NAM in central Canada).


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PRIOR DISCUSSION
~~~~~~~~~~~~~~~~~~

For the next few days, most of the stronger flow aloft will be
restricted north of the US-Canada border, and thus the 500mb
heights across the CONUS generally vary by less than 50 meters at
most locations. Thus, the pattern overall lacks any significant
synoptic forcing and convective processes may be able to drive the
placement of boundaries (and future rainfall) from day to day.

The greatest spread remains just off the east coast where a
weakness in the ridge has supported a developing weak closed low
and surface cyclogenesis.  Here predictability has been low due to
the absolute strength differences in the closed low lead to larger
variation in southward extent and strength of the surface low. 
The UKMET continues to be most aggressive south and therefore
deepest with the surface low, and not likely, the ECMWF/CMC are
equally compact and dig sooner than the 06Z GFS/GEFS and so the
surface reflection lifts north under influence of a slightly
faster approach of the kicker wave.  The 12z GFS however, deepened
slightly and now better matches the ECWMF, likewise the NAM has
moved on par with the GFS/ECMWF but remains a bit east of the two.
  Overall something between the GFS/ECMWF/NAM is preferred but
with continued lower confidence.

Otherwise, the mass fields are fairly agreeable across the CONUS
with the timing of the first frontal zone through the Great Lakes
trailing through the Midwest and Central Plains on Fri thru
Sun...as well as the approach of the next deepening system with
strong frontal push through the northern High Plains/Dakotas on
Sat/Sun.   The UKMET appears a bit fast toward the end of the
forecast period while the CMC appears a bit too slow, typical of
their bias...as such it is suggested to trend away from the
UKMET/CMC Sun.


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

Gallina