Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
105 AM EDT Sun Aug 11 2019

Valid Aug 11/0000 UTC thru Aug 14/1200 UTC

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

00Z Preliminary Model Evaluation with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: 12Z ECMWF/ECENS, 18Z GEFS
Confidence: Average, Slightly below average day 3

Through Wednesday, the synoptic flow will transition from a
middle-CONUS ridge, to nearly zonal flow, to a western
ridge/eastern trough by the end of the forecast period. While the
guidance is nearly uniform in developing this evolution, the
temporal and spatial development varies considerably leading to
lowered confidence, especially into Wednesday.

Initially, a closed low moving into the NW and a shortwave moving
over the SW and atop the ridge will interact to flatten the ridge
into a more zonal pattern. The NAM is north and strong with the
shortwave moving near the Canadian border, and is all alone in
keeping the energy north into Canada. Similarly during this time,
the UKMET continues its summer-long trend of being generally too
strong with the mid-level ridge, in this case keeping the 594dm
heights well longer than any other guidance, and is generally
about 4dm higher with its heights than the remaining guidance.

Later in the forecast, a shortwave will drive a cold front into
the Great Lakes and into the Northeast, amplifying the trough in
the east downstream of the strengthening ridge which backs up into
the Southwest once again. Along this front, there remains a signal
for heavy rainfall in the northern OH VLY and into the Great
Lakes, but the models differ considerably in placement. The GFS
appears too far north, likely due to weaker ridging out west
leading to more subdued troughing in the east, and it is also
inconsistent with itself showing a wide run-to-run variability.
The CMC appears to have the axis of QPF elongated too much to the
southeast, a setup that would be more likely should the trough
become negatively tilted, but in this case remains positive to
neutral.

That leaves the ECMWF and the GEFS/ECENS means as the most
reasonable and middle-ground scenario. While these small scale
features are difficult to discern with high confidence, and the
evolution may change, the consistency of the ECMWF along with the
ensemble support suggest this blend should be reasonable for the
entire CONUS during the next 3 days.


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

Weiss