Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
112 AM EDT Tue Jul 30 2019

Valid Jul 30/0000 UTC thru Aug 02/1200 UTC

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

00Z NAM/GFS Evaluation and Preliminary Preferences/Confidence
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...East of the Mississippi River...
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Preference: General model blend
Confidence: Above average

Mid/upper-level troughing will generally remain over the eastern
third of the nation with a northern and southern stream component.
The northern stream component will track from the Great Lakes this
morning to New England Thursday morning, with a cold front
following along ahead at the surface. A southern stream component
to to the trough will exist as a compact closed upper level low
over the Gulf of Mexico or an elongated trough extending northward
into the Gulf Coast states.

While minor model differences exist with these features, they are
small enough to allow for a general model blend as a preference.


...Pacific Northwest...
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Preference: 00Z NAM/12Z ECMWF blend
Confidence: Average

Outside of the 12Z UKMET, the models have converged closer with
the evolution of the closed low, located just off of the British
Columbia coast this morning, 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. The 12Z UKMET is a slow outlier with
the shortwave trough/closed low nearing Washington/Oregon Friday
morning and the 00Z GFS is a strong outlier. A blend between the
00Z NAM and 12Z ECMWF is closest to the relatively agreeable
ensemble means and will be preferred at this time.


...Southwest into the Great Plains...
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Preference: near the 12Z ECMWF/UKMET
Confidence: Below average

There is generally good agreement on the strength and position of
the southwestern U.S. ridge and on the idea for a convectively
enhanced mid-level vorticity max to round the ridge Wednesday into
Friday...tracking from western AZ to WY into the Dakotas. The
GFS/ECMWF have had the best run to run consistency on the
mid-level vorticity max with greater run to run changes noted in
the NAM, UKMET and CMC. However, downstream into the Plains, the
12Z ECMWF/UKMET show better agreement with an area of low pressure
at the surface in western KS o the latest ensemble scatter low
plot clustering compared to the farther south 00Z NAM/GFS. For
this reason, a 12Z ECMWF/UKMET blend is preferred, but confidence
is low due to the uncertainties with convection and its influences
on impulses rounding the southwestern ridge.


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

Otto