Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1215 AM EDT Fri Sep 20 2019

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

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

00Z Model Evaluation with Preferences and Forecast Confidence
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...Overall Pattern across the CONUS...
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Preference: Blend of the 00Z NAM/GFS and 12Z ECMWF
Confidence: Average

The synoptic pattern will feature a rather strong deep layer ridge
across a large portion of the eastern U.S. over the next couple of
days, as a pair of fairly robust northern stream troughs traverse
the western U.S. The first trough will advance east across the
central/northern Plains and upper Midwest Saturday and Sunday
along with an attendant cold front and a multiple waves of low
pressure. This energy will break down the ridge over the East by
later Sunday and will allow a cold front to arrive across the OH
Valley and lower Great Lakes region by Monday. Meanwhile, a second
upstream trough will cross the West Coast and move into the Great
Basin by Monday.

Differences with the first trough are rather small through most of
the weekend as the energy crosses the Intermountain West and
advances out into the Plains, but by late Sunday, and especially
by Monday, the 12Z UKMET leans toward a somewhat slower and deeper
solution compared to the 00Z GFS and 12Z ECMWF. The GFS though did
trend a bit slower compared to the 12Z cycle. The 00Z NAM is just
a tad more progressive than this consensus, with the 12Z CMC close
timing wise, but becomes deeper than the GFS/ECMWF camp over
Ontario by Monday.

Regarding the second trough, the model guidance is well clustered
until Monday when the 12Z UKMET again favors a somewhat slower
trough. Meanwhile, the 12Z CMC is just a tad more progressive than
the multi-model consensus. The 00Z NAM/GFS and 12Z ECMWF are well
clustered with the system, although the ECMWF is a little deeper
than the NAM/GFS camp.

Based on the latest model clustering and ensemble means, a blend
of the 00Z NAM/GFS and 12Z ECMWF will be preferred both the mass
field evolution of both troughs across the CONUS.


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

Orrison