Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
346 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 Final Model Evaluation, Confidence, and Preferences
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...Overall Pattern Across the CONUS...
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Preference: 00Z GEFS/00Z ECMWF/00Z NAM
Confidence: Average

07Z Update: Little differences noted in the 00Z Non-NCEP suite.
There remains above normal spread in the Northwest late on Day 2
into Day 3 which causes some lowered confidence, but the
preferences remain the same.

Previous Discussion:
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/GFS are very tightly clustered to the 03Z NHC
track into day 2. After 48 hours, the best proxy blend begins to
diverge such that the GFS/UKMET are closest to the NHC track, and
late into day 3 the GFS alone is the best proxy as the UKMET is
too far west, and the ECMWF is too slow. So initially, the 3
models create the closest blend, slowly transitioning to the GFS
on day 3.

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

Weiss