Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
126 PM EDT Tue Jul 30 2019

Valid Jul 30/1200 UTC thru Aug 03/0000 UTC

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

12Z Model Evaluation and Preferences/Confidence
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...Central and Eastern U.S...
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Preference: General model blend
Confidence: Above average

Mid/upper level troughing expected across the eastern CONUS with
ridging building across the Plains.  Models are in fairly good
agreement in terms of mass fields with the timing and placement of
the surface front. The northern stream component of the trough is
certainly helping to push the surface front eastward. Meanwhile
the southern stream, while weak, is due to a closed upper low. The
mid-level impulses rounding the trough in the east, moving atop
the surface front, will likely result in QPF differences.  This is
most notable with the 12Z GFS/00Z UKMET/12Z NAM as vorticity is
stronger among these models, especially compared to the 00Z ECMWF.
However, these differences are fairly small and the ensemble
clustering seems reasonable.

Also, mid-level energy rounding the aforementioned ridging across
the Plains will promote an MCS feature that is depicted by all
model guidance.  The 00Z CMC seems to be a bit farther east as
compared to the rest of the model guidance.  However, the
placement and timing difference are minimal.  And it does appear
the 00Z ECMWF may be holding onto mid-level energy/divergence
aloft a bit longer than the other model guidance across portions
of the Plains on Day 1 which does seem to result in higher QPF
across NE.  However, again, these differences when looking at the
mass fields are not large enough to favor one model over another
as models have shown run to run continuity. 


Therefore, comfortable preferring a general model blend. 


...Pacific Northwest...
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Preference: General Model Blend
Confidence: Average


Models have converged closer with the evolution of the closed low,
located just off of the British Columbia coast, as it reaches the
West Coast. The closed low is expected to move inland into central
British Columbia Wednesday night while a shortwave trough axis,
extending southwest of the closed low, nears the coasts of
Washington and Oregon early Friday morning. A general blend is
closest to the relatively agreeable ensemble means and is thus
preferred at this time.


...Southwest into the Great Plains...
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Preference: near the 00Z ECMWF/UKMET
Confidence: Below average

With the ridge building east into the Plains through the period as
the aforementioned trough approaches the Pacific Northwest, expect
mid-level energy rounding the ridge to be the features of most
concern.  While most of the model guidance is in generally good
agreement with the position of the ridge and the overall idea of
mid-level energy, how this manifest itself in terms of the heights
and propagation is still different among the models.  The 12Z
GFS/NAM show the vorticity a bit farther north and also undercuts
the ridge across the Dakotas. Conversely, the highest QPF among
the GFS/NAM modes is farther south. Meanwhile, the UKMET and ECMWF
show energy and QPF across NE/KS which seems to have a bit more
run to run consistency. Given that the ridge between the troughing
to the west and east, feel the ECMWF/UKMET are still preferred at
this time. 


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

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