Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
115 AM EDT Sun Sep 01 2019

Valid Sep 01/0000 UTC thru Sep 04/1200 UTC

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

00Z Preliminary Model Evaluation, Confidence, and Preferences
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...Overall Pattern Across the CONUS...
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Preference: 18Z GEFS/12Z ECMWF/00Z NAM
Confidence: Average

The overall synoptic pattern will persist with a ridge in the west
and a trough in the east. While the guidance is well clustered in
the broad evolution, there are significant differences that arise
in day 2, and even moreso on day 3, across the NW and northern
tier. A shortwave moving into the PacNW will eject eastward Monday
into Tuesday, with shortwave ridging developing quickly in its
wake. The CMC is very quick to push this energy eastward,
outpacing the global consensus considerably. The GFS is on the
other side of the spectrum, with the shortwave moving so slowly
that it hangs back and cuts off into a mid-level low where the
remaining guidance has upstream ridging. This seems unlikely as
the flow across the northern tier is modestly fast embedded within
a 90 kt upper jet. The UKMET is usable, but its heights are a few
dm higher as it maintains the strength of the ridge more strongly
than the remaining guidance. The new NAM looks very much like the
ECMWF and the 18Z GEFS mean, bringing some consistency to
otherwise messy 60-84 hour mass fields.


...Hurricane Dorian...
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Please refer to the official National Hurricane Center forecast
track

The ECMWF/UKMET are very tightly clustered to the 03Z NHC track
into day 2. Beyond that, the ECMWF slows considerably and nearly
stalls near the Bahamas, and the NHC track becomes more aligned
with the 00Z GFS and the 12Z UKMET. This suggests a blend of the 3
gives something close to the official track, but utilizing more
weight on the ECMWF early, leaning more on the GFS late.

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

Weiss