Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
306 AM EDT Sun Jul 21 2019

Valid Jul 21/0000 UTC thru Jul 24/1200 UTC

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

00Z Final Model Evaluation Including Preference and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General Model Blend
Confidence: Slightly Above Average

07Z: The 00Z Non-NCEP suite has all slowed with its eastern CONUS
trough development, which is reasonable based on the intensity of
the ridge preceding it. The CMC which was a fast outlier is now in
line with the ensemble means, and the ECMWF/UKMET look similar to
the NAM with the slower frontal progression and trough axis
position. While small differences exist in shortwave impulses
moving atop the ridge the first 36 hours, as well as the
wavelength of the ridge building northward from the Four Corners,
a general model blend should be sufficient until the finer scale
details can be resolved.

Previous Discussion:
Synoptic regime change occurs in the short term as expansive ridge
producing excessive heat across 2/3 of the CONUS gets gradually
displaced by a deep longwave trough across the east, reorienting
the amplified ridge into the west. Although slight differences
exist initially among the global suite as to position and
intensity of shortwaves rotating atop the periphery of this ridge,
a general model blend could be used for the first 36 hours.

Thereafter, changes arise as the CMC is fast driving the trough
and surface cold front into the east, far outpacing the remaining
guidance and ensemble means by Tuesday. The NAM is too amplified
with this trough compared to the remaining guidance, a trend that
has been noted repeatedly over the past few days. While the GFS is
a bit faster with the frontal progression than the preferred
UKMET/ECMWF which are in good agreement, its mass fields are well
within the ensemble envelope by Tuesday with the position of the
trough axis and can be utilized in the blend. Across the west, a
closed low diving into the PacNW will shorten the wavelength of
the ridge across the Mountain West, but timing and intensity of
the different models are in good agreement, and no changes to the
blend are needed.


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

Weiss