Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
253 PM EDT Mon Aug 12 2019

Valid Aug 12/1200 UTC thru Aug 16/0000 UTC

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

12Z Model Evaluation with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of the 12Z GEFS mean/00Z ECENS mean
Confidence: Below Average

The synoptic evolution through the forecast period is generally
well agreed upon by the global suite, but smaller scale features
create discrepancies in the sensible weather and synoptic
evolution leading to a lower than average confidence forecast.

The UKMET continues to occasionally be somewhat of a stronger
outlier with its ridging across the southern U.S. through the
period, but the guidance does all agree on gradually advancing a
portion of the ridging westward into the Southwest. Meanwhile, a
series of relatively low-amplitude shortwaves will advance across
the Midwest, Great Lakes and into the East through the period
which will carve out a broad longwave trough involving much of the
northern and eastern U.S. The NAM overall is a little stronger
than the model consensus with the shortwave energy, and the UKMET
is on the weaker side. The GFS, CMC and ECMWF are clustered in
between.

All of the models allow a cold front to advance through the
Midwest and into the East over the next few days, and the models
have come into a bit better agreement with the 12Z cycle as the
ECMWF and CMC have trended a little farther south toward the NAM
and GFS camp by the end of the period as the front stalls over
portions of the Mid-Atlantic and Southeast. Overall, the UKMET
probably has its front a tad too far south, but the difference is
rather modest compared to the model consensus. All of the models
also have an elongated area of low pressure focused along the
front over the Southeast, along with a separate weak low center
over the OH Valley. The NAM appears to be perhaps a tad stronger
with this OH Valley low compared to the global models, but this
appears to be related to the NAM having slightly stronger height
falls.

There is also spread across the Northwest by the end of the period
as the guidance favors a shortwave trough dropping in toward the
Pacific Northwest. The GFS and UKMET are the most progressive with
the CMC the slowest.

Based on the model spread in the details of the energy in the
Northwest and to some modest extent along the East Coast by the
end of the period, a blend of the ensemble means will be preferred
which are in reasonably good agreement across most of the CONUS.
Although it is noted that the 00Z ECENS mean is a bit stronger
than the most of the deterministic models and the 12Z GEFS mean
across the Northwest at the end of the period.


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

Orrison