Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1222 AM EDT Mon Sep 09 2019

Valid Sep 09/0000 UTC thru Sep 12/1200 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: Non-NAM Blend; more weight on 12Z ECMWF, UKMET
Confidence: Average

Models very consistently show an amplification of the synoptic
pattern over the next couple days, with a trough in the western
U.S. and a ridge in the East, with zonal flow through the Great
Lakes and Northeast. Differences begin to emerge with the trough
as it pushes from the Intermountain West into the Northern Plains
on Wednesday and Wednesday Night.

The 00Z NAM was excluded from the preference, as it has lower
heights in the base of the trough as it moves through the West,
and this eventually leads to a stronger and slower mid-upper level
low by mid-week. This does not have much ensemble support.

Otherwise, deterministic models show some spread with the timing
and sharpness of the trough (amplification of upstream and
downstream ridges), but isoheights aloft are within the ensemble
envelope. By Thursday morning (12.12Z), an even blend of the
deterministic models seems somewhat under-dispersive. There are
numerous ensemble members (ECMWF and NAEFS) that have a slower
trough progression and a more amplified downstream ridge over
Manitoba and western Ontario. The 12Z and 18Z GEFS ensemble mean
is considerably different from the operational 00Z GFS. Because of
this, the preference is for a non-NAM blend overall that places
greater weight on the 12Z ECMWF and UKMET, as they are more
representative of the ensemble means.


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

Lamers