Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
334 PM EDT Mon Sep 09 2019

Valid Sep 09/1200 UTC thru Sep 13/0000 UTC

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

12Z Final Model Evaluation with Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: 12Z GEFS mean/12Z ECMWF/UKMET/00Z ECENS mean
Confidence: Average

19Z Update: The general trend in the 12Z global suite was to
become subtly more amplified with the trough-ridge pattern across
the CONUS. The overall spread remains minimal, with the exception
being that the 12Z CMC has trended towards the 12Z NAM, which are
now both too quick to close off the upper low, and too deep with
the heights in the base of the trough moving through the Rockies
on day 3 /Thursday/. Otherwise, the guidance is well clustered
with the ensemble means, so the blend remains minimally changed.

Previous Discussion:
The global suite is in very good agreement in the synoptic
longwave pattern through the next 3 days with an amplifying trough
across the west and an expansive ridge in the east. The exception
will be across New England where a shortwave will move across
Maine bringing somewhat lowered heights on the northern periphery
of the ridge Wednesday into Thursday.

In the east, both with respect to the ridge and the shortwave
trough in New England, the guidance features very little spread
overall. This suggests a general model blend can be incorporated
for all points east of the Rockies. In the west, the discrepancies
become more significant, especially day 2 into day 3 /Wednesday
and Thursday/. The NAM is very quick to close off the trough
across the Northern Rockies, which forces lowered heights through
the base of the trough moving eastward into Thursday. This stands
out as a clear outlier. The 12Z GFS is also fast to close off a
mid-level low, and while its heights are reasonable through the
trough, it is amplified compared to the remaining guidance and to
its 06Z GEFS mean. With little spread amongst the 06Z GEFS and the
full suite of 00Z Non-NCEP models, the preference hedges in that
direction for better consistency and a more realistic solution as
the shortwave moving through Maine should at least slow the
amplification /closing off/ of the trough in the west.

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

Weiss