Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
104 PM EDT Sun Sep 29 2019

Valid Sep 29/1200 UTC thru Oct 03/0000 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 Pattern Across the CONUS...
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Preference: General model blend, lower weight on 12Z GFS, NAM
Confidence: Slightly above average

Models continue to be in very good agreement over the next few
days with the synoptic pattern. A blend of the available
deterministic models should represent the ensemble spread
reasonably well and account for a variety of scenarios associated
with small differences.

The most notable differences seem to be related to the mid-upper
level low in the Northern Rockies and how that ejects out to the
northeast by mid-week. The 12Z GFS and NAM maintain a stronger,
closed low while the remaining global models (00Z ECMWF, UKMET,
CMC) show the low opening up into a wave and getting sheared out.
These other models tend to be stronger with the ridge through the
Upper Midwest and Great Lakes, and this scenario (represented by
ECMWF, UKMET and CMC) is given greater weight in the preferred
model blend.

The biggest impact to QPF seems to be that the stronger low and
erosion of the northern cusp of the ridge in the GFS and NAM cause
the axis of heavy rainfall to shift further east in the Plains by
Day 3, while other models are more focused.


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

Lamers