Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
237 AM EDT Wed Jul 04 2018

Valid Jul 04/0000 UTC thru Jul 07/1200 UTC

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

00Z Model Evaluation including preference and forecast confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Model Assessment over the CONUS...

Preference: General model blend through 06/12z;
            Non-CMC blend in Pacific Northwest
            00z ECMWF/GFS blend in the Southeast
Confidence: Above average; Average on day 3 in Southeast

07z Update Discussion:

The 00z ECMWF reentered the inner core of the closed low/surface
low northward earlier Fri/Sat but with only exception of the 00z
CMC, all other guidance caught back up and showed similar
timing/shape to the trof entering the NW by late Fri into Sat. 
Elsewhere, the CMC did handle the secondary TUTT cell more in line
with the remain guidance but like the NAM and the prior run,
becomes a bit more strung out across the Eastern Gulf to FL and by
Sat is out of phase/shape with the GFS/ECMWF which are a bit more
favored.  The 00z UKMET generates a compact and strong third TUTT
cell east of the GA coast by Sat, out of tolerance.  As such
favoring the 00z GFS/ECMWF in the Southeast after 06/12z is
suggested...non-CMC in the Northwest after 06/12z as well.  Still
confidence is above average for the larger scale (perhaps average
in Southeast) 

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PRIOR DISCUSSION
~~~~~~~~~~~~~~~~~~~~~
The dominant weather pattern is the strengthening and westward
migration of a nearly continental wide ridge that eventually
reaches the Central Rockies by Fri with 600 dekameter heights. 
The compact shortwave currently over the Northern Rockies over
tops the ridge and extends southward into the Great Lakes and
Northeast Thursday into Fri splitting the ridge allowing for
southerly flow ahead of the frontal zone toward the end of the
forecast period.   Here the guidance is fairly agreed upon with
small timing/depth differences especially as the frontal
zone/mid-level trof splits through the Mid-Atlantic and some
energy begins retrograding into the Upper-Tennessee Valley Sat.  
Here the NAM and the CMC may be a bit more aggressive with phasing
with some trailing energy with a TUTT cell along the Northeast
Gulf coast.

Along the base of the ridge, a smaller more compact TUTT cell
currently near LA will shift west and flatten into the northern
Sierra Madre and remain in Mexico, there is good guidance
agreement with this feature.  The aforementioned (paragraph above)
secondary TUTT is a bit stronger/broader and shifts through FL
late today into Thurs and is fairly well agreed upon at least
initially.  Eventually, the 00z NAM is flatter and more strung out
back into the Sargasso Sea, which by Sat starts to form into a new
wave.  This is supported by the GFS but not many others, and is
likely the highest uncertainty and lowest confidence in the
overall preference.    The 12z CMC becomes quite amplified with
the second TUTT cell south of LA by Sat while most of the guidance
has translated the wave west toward the TX coast. 

The 12z CMC has some late forecast period model/timing differences
with respect to the developing closed low off the West Coast as it
unfolds and lifts toward Vancouver Island on late Fri into Sat. 
The CMC being typically slow, allows for the lingering base to
stall relative to the ECMWF/GFS/NAM and ensemble suite, which is
also stronger as it reaches NW CA/SW OR by the end of the forecast
period.  While the surface pattern is not as clearly affected the
mid to upper level flow clearly departs from an otherwise strong
agreement.

With little run to run variation or departure from the 18z
GEFS...the 00z NAM/GFS continue to suggest supporting a general
model blend up until 12 to 18z on Friday the 6th at above average
confidence.  Afterward, favoring shifts away from the 12z CMC is
suggested also at above average confidence.   Please note: the 12z
UKMET was nearly identical to the 03/00z run, due to some
technical issues at the UKMET.  This may not be ideal, but the run
did not depart significantly from the overall model
preference...suggesting good predictability of the larger scale
pattern as a whole providing confidence in the blend, and may be
included to a blend if desired. 


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

Gallina