Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
140 PM EDT Sun Sep 02 2018

Valid Sep 02/1200 UTC thru Sep 06/0000 UTC

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

12Z NAM/GFS evaluation...with preliminary preferences and
confidence
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...Overall Synoptic Pattern across the CONUS...
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Preference: 12Z NAM/12Z GFS/00Z ECMWF blend across the CONUS
            ...see below section for the Gulf of Mexico
Confidence: Average

The more significant differences across the CONUS involve a
moderately strong shortwave to track across south-central Canada
on Tuesday. At the surface, a cold front will move into the upper
Mississippi Valley, extending southward into the central Plains
for Tuesday. The 12Z GFS trended much faster with the 500 mb low
over Manitoba on Tuesday and is also a bit faster with the cold
frontal progression across the CONUS. In addition, the 12Z GFS is
weaker with the magnitude of the upper level jet on Tuesday over
the central to northern Plains. The 12Z NAM/00Z ECMWF appear to be
a better fit across the central Plains/upper Midwest with this
system, with the 00Z ECMWF a bit slower. The 12Z GFS may have
utility across other portions of the CONUS and fits in with a
blend when used with the 12Z NAM and 00Z ECMWF.

...Possible tropical cyclone in the Gulf of Mexico
Tuesday/Wednesday...
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Preference: near the 00Z ECMWF
Confidence: Average

NHC has an 80 percent chance of tropical cyclone formation within
the next 5 days across the northern Gulf of Mexico, tied to a
tropical wave currently tracking west-northwest over the Bahamas.
Ensemble clustering has become a little better over the past 4
ensemble cycles, but weighted most with ECMWF members, and agrees
with the latest deterministic consensus of models, excluding the
12Z NAM which is weaker and faster with the system. The 00Z
UKMET/CMC also agree on the idea of a low center by
Tuesday/Wednesday but are on the stronger side of the model
spread. While the 12Z GFS agrees with the timing of the non-NAM
deterministic consensus, it is a bit farther north/inland with the
low/wave track into Wednesday and weaker. Therefore, the 00Z ECMWF
appears like the best compromise at this point in time. Please
refer to NHC products for the latest on this system.


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

Otto