Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Sat Sep 22 2018

Valid Sep 22/1200 UTC thru Sep 26/0000 UTC

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

12Z Model Evaluation...with Preferences and Forecast Confidence
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...Overall preference for the entire CONUS...
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Preference: General model blend
Confidence: Slightly above average

The models are overall in very good agreement with the evolution
of the large scale flow pattern across the CONUS which is expected
to transition from a rather zonal flow regime initially to a much
more amplified pattern by early next week as a deep long wave
trough develops across the Plains. A subtropical ridge will be
noted off the southeast coast of the U.S. by next Tuesday, with an
attempt at a rex-block developing off the West Coast at the same
time.
of the northern stream flow across the CONUS.

The models show only modest timing/depth spread with respect to
the wave of low pressure that should lift up across the northern
Plains and upper MS Valley Sunday night and Monday. Regarding the
cold front, by the end of the period, the 12Z NAM and 12Z CMC are
a little faster to drive the front southeast across the middle MS
Valley and southern Plains versus the 12Z GFS and more so the 12Z
ECMWF. The 12Z UKMET is generally in between camps. A multi-model
blend will be recommended to resolve these differences here. With
respect to the lingering mid level low currently over the southern
Plains and lower MS Valley, this system should gradually weaken
and begin to dampen out over the next couple of days as multiple
shortwave impulses shear out off to the northeast across the TN
Valley and Mid-Atlantic region. The only other feature of
particular note is an area of low pressure and an associated
trough axis that is expected to approach the Carolinas on Tuesday.
The models are all generally well clustered with this feature,
although the 12Z UKMET was a tad deeper and a little slower than
the model consensus with the low.

Based on the latest model clustering, trends and ensemble
guidance, a general model blend will be preferred with all of
these features and the large scale pattern across the CONUS.


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

Orrison