Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Tue Aug 20 2019

Valid Aug 20/0000 UTC thru Aug 23/1200 UTC

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

00Z Model Evaluation...Including Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 00Z GEFS/12Z ECENS means
Confidence: Average

Mid to upper-level ridging will persist for the next couple of
days from the south-central to the southwest U.S., before the
ridging breaks down as a result of a split flow pattern that
develops across the CONUS. The northern stream energy will
actually become increasingly amplified featuring two troughs, one
over the Pacific Northwest and another across the Midwest and
Great Lakes region. South of the belt of the westerlies will be a
southern stream featuring energy that digs into the Southwest by
later Thursday and Friday, and with a smaller scale shortwave
trough crossing the central Plains by that time.

Overall, the 00Z NAM tends to be a tad more amplified than the
global models with the northern stream trough impacting the
Northwest. The 00Z ECMWF trended a bit weaker from its 12Z run
which was more amplified, and so now the ECMWF is much more in
line with the model consensus. It should be noted that the 00Z
UKMET gradually becomes a weaker outlier as this energy ejects out
across the northern High Plains and crosses through southwest to
south-central Canada. Downstream across the Midwest and Great
Lakes, the 00Z NAM and 00Z CMC solutions gradually lag the
progression of the trough, and the CMC also gradually becomes a
more amplified outlier. However, with respect to the deep closed
low over southeast Canada, the guidance is reasonably well
clustered, although at the end of the period the CMC and to some
extent the UKMET were showing a bit faster closed low evolution
across Quebec.

Elsewhere, the NAM was noted to be a bit deeper with shortwave
energy advancing across the OH Valley and Mid-Atlantic region on
Tuesday and Wednesday. With respect to the southern stream energy,
the NAM was also seen as being a bit deeper than the global models
with both the energy over the Southwest and over the
central/southern Plains toward the end of the period. The NAM also
is the most aggressive of all of the models with energy and
possible low development over the Gulf of Mexico that rides
northwest up toward the southeast TX and LA coastal plain area by
Friday.

For the time being, the preference will be to lean toward a
consensus of the ensemble means for the CONUS per the 00Z GEFS
mean and 12Z ECENS mean to account for some of the regional model
spread, and especially with respect to the troughing ejecting out
toward the northern High Plains 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