Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
242 PM EDT Sat Jun 29 2019

Valid Jun 29/1200 UTC thru Jul 03/0000 UTC

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

12Z Model Evaluation...with Confidence and Preferences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
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Preference: Non-NAM blend...Upper Midwest/Great Lakes
            General model blend...remainder of CONUS
Confidence: Slightly above average

Models remain in fairly good agreement overall through the next
few days with a relatively persistent pattern consisting of a
broad ridge over much of the CONUS, but with troughs over the in
the Northwest and Northeast, and an upper level low drifting
westward underneath the ridge over Texas. Model spread is
generally limited on the large scale with the forecast mass fields
and showing reasonably good clustering.

However, one area of some concern does is involve the placement of
a quasi-stationary frontal zone and evolution of a wave of low
pressure riding east-northeast along it involving the upper
Midwest and Great Lakes region from 12Z/01 through 00Z/03. The 12Z
GFS and especially the 12Z NAM tend to allow the front to gain a
bit more latitude than the 12Z non-NCEP guidance. This is a result
of the NAM/GFS solutions having a stronger mid-level shortwave
impulse ejecting east across the northern Plains which results in
a somewhat stronger wave of low pressure developing along the
front. The NAM overall is the strongest solution and farthest
north with the boundary. The ensemble spread of guidance suggests
little support for the stronger NAM solution at this point, and
even a solution a bit weaker than what the GFS favors.

Based on the latest clustering of solutions and ensemble spread, a
general model blend will be preferred across the CONUS, with
exception to the upper Midwest and Great Lakes where for now a
non-NAM blend will be preferred.


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

Orrison