Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1204 PM EDT Sun Jul 22 2018

Valid Jul 22/1200 UTC thru Jul 26/0000 UTC

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

12Z model evaluation including preferences and forecast confidence
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Preference: Non-CMC blend
            12z NAM and 00z UKMET/ECMWF after 25/00z in northern
tier
Confidence: Slightly above average to average after 25/00z.

The closed low over the Ohio valley to southeast will continue to
fill and remain elongated between the developing subtropical ridge
in the Northwest Atlantic and the large concentric high in the
desert southwest that extends into the Southern Plains; guidance
is strongly agreeable in the mass fields and surface features even
with the muddled/complexities related to such a vast/breaking down
upper level trof.  The 00z CMC is a bit out of phase being a bit
deeper and slower to fill through the end of day 3.

Elsewhere, the deep low tracking across southern Canada still
shows some modest spread, as the 12z NAM/GFS both remain a bit
stronger (closer to current observations) in the mass fields
further south and east compared to the ECMWF/UKMET.  Still, the
timing and depth of the frontal zone look good for this portion of
the system to be considered for a general model blend.  It is the
variance Tues into Wed, when an Arctic stream shortwave rotates
around the western periphery of the remaining upper low bringing
another frontal zone southward.  Here the GFS and NAM followed by
the UKMET are faster bringing the front and reflect a stronger
surface wave into MN/SW Ontario by late Wed.   While the 12z GFS
backed off on the compact nature of this wave, it is even faster
than that NAM/UKMET by 00z Thurs.  The 00z CMC is also very slow
with this wave out of the Arctic stream as well, almost locking to
the terrain along the BC/Alberta line around 00z Tues.  As such
will favor backing away from the GFS after 25/00z but Non-CMC
throughout the forecast period.   Confidence is slightly above
average (especially over the eastern third of the continent, but
breaks down to average across the northern tier on Day 3.

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


Gallina