Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
229 AM EDT Mon Aug 19 2019

Valid Aug 19/0000 UTC thru Aug 22/1200 UTC

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

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

The main component of mid-upper level ridging in place at the
start of the period near the Rio Grande will translate westward to
just off of the Southwest coast by Wednesday afternoon. A small
portion of the ridge will remain over the south-central U.S.
Meanwhile, across the northern tier of the U.S., the flow is
quasi-amplified with a closed low over south-central Canada which
will track east and elongate east-west before re-amplifying
southward toward the Great Lakes late Wednesday. Back to the west,
an anomalous upper trough, forecast to be offshore of the Pacific
Northwest on Tuesday, will weaken slightly as it moves into
British Columbia and the Pacific Northwest Wednesday.

There are some minor timing differences with the upper trough in
the vicinity of the Great Lakes, but there are more concerns
regarding the depth of it. Firstly, the 00Z NAM appears to be a
tad too strong with some of the vort energy advancing east
underneath the trough as it crosses the OH Valley, Mid-Atlantic
and Northeast Tuesday and Wednesday. Regarding the larger scale
trough, the 00Z GFS becomes the strongest solution, with the 00Z
CMC the weakest. This translates accordingly to the same intensity
spread with the evolving surface low impacting southeast Canada.
Meanwhile, the 00Z ECMWF is seen as placing it surface and
mid-level low centers on the south side of the model consensus and
south of the 12Z ECENS mean. The 00Z GEFS mean is rather close to
the 12Z ECENS mean with this evolution, and suggests the
deterministic GFS is a strong outlier.

Farther south across the eastern Gulf Coast and the Southeast, the
00Z UKMET is still a bit of a strong outlier with the slowly
meandering low/mid-level low center near the FL Panhandle and
southern GA. The guidance overall suggests this energy will
gradually elongate and shear slowly off to the northeast over the
next couple of days across the Southeast.

Across the Pacific Northwest, the 00Z NAM and 00Z CMC are a bit
slower than the multiple model consensus, and also are a bit more
aggressive with their height falls versus the 00Z GFS and 00Z
ECMWF, although the GFS is a tad stronger and faster than the
ECMWF. Both the GFS and ECMWF are well supported by their
respective ensemble means regarding the depth and timing of this
system.

Based on the latest model spread, ensemble clustering and trends,
a blend of the ensemble means will be preferred across the CONUS
via the 00Z GEFS and 12Z ECENS means which should help to resolve
of the regional differences seen in the guidance.


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

Orrison