Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
227 AM EDT Wed Aug 21 2019

Valid Aug 21/0000 UTC thru Aug 24/1200 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 through Wednesday 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 a bit more amplified with two troughs of note. One
will impact the Pacific Northwest and northern Plains, with
another one over the Great Lakes region and Northeast. 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/southern  Plains and the lower MS Valley through Friday
and Saturday.

Overall, the 00Z NAM is a bit more progressive than the global
models with the troughing that ejects east across the northern
Rockies and High Plains by Friday, however, the 00Z ECMWF/CMC
solutions are the slowest solutions and also tend to be the
deepest. The 00Z UKMET is only a little more progressive than the
ECMWF/CMC camp, but the 00Z GFS splits the difference between the
faster NAM and the slower non-NCEP camp.

Downstream across the Great Lakes and Northeast, the models show a
fair degree of trough amplification and also drive a cold front
southeast across the OH Valley, Mid-Atlantic and Northeast. The
guidance is reasonably well clustered with this, but the 00Z UKMET
is a bit weaker than the remaining guidance.
 
Elsewhere, regarding the southern stream energy, the 00Z NAM is
seen as being a bit deeper than the global models with a focus in
particular on the energy over the central/southern Plains. The 00Z
GFS is also a bit on the deeper side of the guidance and is seen
as being slower with the shortwave evolution. The GFS is also a
bit deeper than the remaining guidance with the weakness that is
over the Southwest. Regarding the weak disturbance/trough lifting
northwest across the western Gulf of Mexico by Thursday and
Friday, the NAM overwhelmingly sticks out as a strong outlier
solution as it develops a well-defined low to mid-level low
center, and has a very strong QPF signal impacting southern LA.

For the time being, the preference will be to lean toward a
consensus of the 00Z GEFS mean and 12Z ECENS mean across the
CONUS. This will provide a strong and well clustered compromise
solution with the details especially concerning the trough
crossing the Northwest and the northern Plains, and will help to
better resolve some the smaller scale spread seen with the
southern stream shortwave energy.


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

Orrison