Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Thu Oct 03 2019

Valid Oct 03/0000 UTC thru Oct 06/1200 UTC

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

00Z Final Model Evaluation with Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: Non-CMC. Heavy weight on ECENS/GEFS day 3.
Confidence: Slightly above average

07Z Update:
There exists a significant dichotomy between the NCEP and Non-NCEP
guidance with the shortwave dropping through the Northwest to
reinforce the longwave trough on D3. The NAM/GFS are much sharper
and slower with the shortwave, while the UKMET/ECMWF are flatter
and faster. The Non-NCEP guidance is much closer in their
solutions to both the ECENS mean as well as the GEFS mean, lending
support to this faster/weaker shortwave solution. For this reason
will make no change to the preferred blend, while still excluding
the CMC for its anomalous 300mb jet behavior.

Previous Discussion:
Through 48 hours, the guidance is in very good agreement with a
ridge in the east slowly breaking down while a trough digs into
the west and ejects quickly into the Northern Plains while taking
on a negative tilt. The exception to this is the 12Z/2 CMC which
is vastly different, and is likely in response to much different
northern/subtropical jet energy phasing across the middle of the
country. This interaction is leading to much different amplitudes
of the trough-ridge across the CONUS and is well out of tolerance
with the remaining suite and consensus.

More significant spread develops after 60 hours with the
negatively tilting shortwave lifting into the Great Lakes as well
as secondary vorticity energy /shortwave/ digging to reinforce the
trough across the PacNW D3. The ECMWF is quite amplified with the
lead shortwave compared to the remaining guidance, and while the
amplitude spread is not significant, the op ECMWF is much deeper
than the ECENS mean or any other model so should be used carefully
in the Northern Plains/Great Lakes. For the trailing shortwave,
spread becomes more robust as the GFS/NAM are sharper, while the
ECMWF/UKMET are flatter. The issues with the ECMWF in the lead
shortwave cause some concern using the latter shortwave, so a
trend towards the ECENS/GEFS mean is most reasonable at the end of
the forecast period.


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

Weiss