Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
341 PM EDT Mon Sep 30 2019

Valid Sep 30/1200 UTC thru Oct 04/0000 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 non-CMC/NAM blend central/east, non-GFS on Day 3
on West Coast
Confidence: Average

The main two concerns in the next three days are timing of the
trough currently over the Northwest CONUS as it ejects northeast
across the northern Great Plains late Wednesday/the northern Great
Lakes Thursday and the next trough digging into the West Coast on
Thursday.

The 12Z NAM remains the fastest to eject the trough with
differences appearing in Day 2 and continuing to outpace the 12Z
consensus through Day 3, so it is not a part of the blend. The 12Z
CMC is deeper and slower with the low over the northern Great
Lakes on Day 3, so it also is removed.

The 12Z GFS continues a long trend in the GFS of having a
shallower trough in The West on day 3 which results in
precipitation limited farther north (noticeable over OR) compared
to the 12Z consensus which is consistent among all other guidance.
Therefore, a non-GFS general model blend is recommended in The
West for Day 3.

The 12Z ECMWF and UKMET share strong similarities in how they
advect the strong shortwave trough as it rounds and tops off
eastern CONUS ridge as well as a more amplified trough down the
West Coast on Thursday. These models are preferred at this time
with the other models at lower weights.

A heavy rain event across the middle of the country is still
expected through Wednesday night as the trough taps gulf moisture
and plenty of energy from the above normal temperatures that have
been pervasive under the ridge centered over the eastern CONUS.


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

Jackson