Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1232 PM EDT Wed Sep 25 2019

Valid Sep 25/1200 UTC thru Sep 29/0000 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, strongest weight to ECMWF, GFS
Confidence: Slightly above average

Models are in excellent agreement on a major pattern shift in the
next few days, with a trough digging into the Northwest on Friday
and amplifying over much of the West on Saturday. This will enable
considerable amplification of the downstream ridge in the eastern
half of the CONUS by the weekend.

The global models seem to be close in their timing of the trough,
with most of the spread concentrated at the base of the trough.
This suggests the primary differences are related to trough
amplification, and the 00Z UKMET is most difference in this
regard. It shows much less amplification than the other global
models, but is still joined by a few ensemble members. Therefore,
it's not impossible, but the preference is to lean in the
direction of much greater ensemble support close to the 12Z GFS
and 00Z ECMWF.

The 12Z NAM shows greater timing differences, and is generally
faster with the trough than the global models. This also seems
less likely, given the relatively strong timing agreement from the
global models.

It's worth noting that there were a considerable portion of the
00Z ECMWF ensemble members that were more amplified with the
trough (and downstream ridge) than the 00Z GFS and 00Z ECMWF.
However, the 12Z GFS did produce a more amplified trough than its
00Z run, so an additional trend toward more amplification is
possible from the remaining models.


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

Lamers