Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1247 PM EDT Sat Sep 07 2019

Valid Sep 07/1200 UTC thru Sep 11/0000 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: 12Z NAM/GFS blend...Plains/Midwest
            General model blend...remainder of CONUS
Confidence: Average

The models are in good agreement with the large scale synoptic
evolution across the CONUS over the next few days. This will
involve the amplification of a deep trough across the West by
Tuesday, and a rather strong deep layer ridge over the Southeast.
Meanwhile, the deep troughing over the Northeast over the next 1
to 2 days which captures the rapidly departing Hurricane Dorian
approaching Nova Scotia will lift northeast across southeast
Canada with time and allow for steady height rises in its wake.

As the larger scale flow becomes more amplified with time, the
guidance takes the initial shortwave trough ejecting out across
the northern Plains today off to the east and across the upper
Midwest through Sunday while gradually dampening it out. The model
differences with this system are modest with the 12Z NAM and 12Z
GFS just a tad more amplified and a little slower than the 00Z
non-NCEP camp of guidance including the UKMET, CMC and ECMWF.
Meanwhile, a negatively tilted trough crossing the West Coast
later today will advance into the Intermountain region on Sunday.
On Monday, this system will progressively cross the central and
northern Plains and begin to dampen out as it encounters
increasingly confluent mid/upper-level flow downstream. There are
some notable timing differences with this feature as the 12Z NAM
and 12Z GFS have both trended a bit more progressive with the
energy as it ejects out across the Plains, and are both faster
than the 00Z non-NCEP suite of guidance. This drives the NAM and
GFS to have a more progressive surface low evolution, and has a
direct impact on the model QPF, especially by late Monday into
Tuesday across the upper Midwest and Great Lakes region.

The preference will be to lean toward a blend of the NAM and GFS
with all of the shortwave energy impacting the central/northern
Plains and Midwest through the period. However, a general model
blend should suffice elsewhere given strong multi-model
clustering/agreement.


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

Orrison