Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1236 AM EDT Fri Jul 20 2018

Valid Jul 20/0000 UTC thru Jul 23/1200 UTC

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

00Z GFS/NAM evaluation with preliminary model preferences
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Convective frontal wave emerging from Southeast
and moving up the Eastern Seaboard Saturday & Sunday
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Preference: 18z GFS/12z ECMWF compromise
Confidence: Below average

The guidance takes what has been a broad convective frontal wave
(with very high precipitable water values) moving across the
Southeast over the past couple of days and move it to the coast
Friday afternoon, which spurs various forms of convective
redevelopment/gridscale feedback in the guidance.  The 12z UKMET
is by far the strongest with this system.  The 12z Canadian and
00z GFS are the quickest and along with the 00z NAM, most westerly
with this system.  The National Hurricane Center believes any
tropical cyclone development potential here is low, which is
supported by GFS and Canadian-derived simulated satellite imagery
which shows a low with a developing comma head moving up the East
coast from late Saturday onward (when north of the Gulf Stream). 
The 12z global ensemble guidance and the 18z GEFS mean show decent
clustering on a slower and more coastal track, which resembles a
compromise of the 18z GFS and 12z ECMWF, although a slightly
stronger solution is possible.  This solution is preferred for now
with below average confidence. considering the guidance spread in
track and depth.


System moving across the Northwest & Northern Plains
Upper trough/low dropping southward into the Southeast
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The guidance shows good agreement with these features, thus a
compromise of the 00z GFS, 00z NAM, 12z UKMET, 12z Canadian, and
12z ECMWF is preferred with above average confidence.

Roth