Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
242 AM EDT Thu Aug 01 2019

Valid Aug 01/0000 UTC thru Aug 04/1200 UTC

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

00Z Model Evaluation and Preferences/Confidence
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...Overview of the CONUS features...
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Preference: General model blend
Confidence: Average

The main forecast issue for this time period is the short wave
energy riding over the top of the mid level ridge that moves
slowly westward across the Four Corners area through Day 2. The
00Z NAM was further west with the short wave energy (as was to
some extent the 00z GFS) into the Central Plains and Mid MS Valley
through 03/00z. The 00z NAM/GFS remain further south and west with
the track of the short wave energy and surface frontal position in
proximity of the mid level ridge into Day 3 across the Lower MS
Valley into the Southern Plains.

The non-NCEP guidance (00z ECMWF/CMC/UKMET) has trended toward the
NCEP guidance with the placement of the frontal boundary and short
wave energy, though the 00z GFS/00z GEFS may be too far south by
the end of Day 3. This shift has allowed the differences in the
QPF axes to cluster better with the expected MCSs, though there
could still be some longitudinal differences with the eastern edge
of the mid level ridge and capping.

Across the Northeast and Quebec, there is generally good model
agreement with the evolution of the mid level closed low, so a
general model blend is preferred here as well, as operational
models cluster well with the ensemble means.

There is better model agreement with  the timing of the positively
tilted long wave trough extending across British Columbia into the
Pacific Northwest, with only the 00z CMC being faster with the
trough. Since the impact with respect to sensible weather for the
Pacific Northwest is minimal, a general blend is preferred here.

Finally, a surface trough or weak surface wave off the southwest
FL coast from late Day 1 into early Day 2 becomes involved with an
area of disturbed with over the Bahamas, and the surface
reflection then tracks off the Southeast United States coast
during Day 3. The 00z UKMET/CMC are in good agreement with the 00z
NAM/GFS with the positioning of the surface feature, so a general
model blend was preferred here.

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

Hayes