Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1234 PM EDT Wed Aug 28 2019

Valid Aug 28/1200 UTC thru Sep 01/0000 UTC

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

12Z Preliminary Evaluation with Preferences and Forecast Confidence
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...Overall Pattern Across the CONUS...
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Preference: Non-CMC blend
Confidence: Slightly above average
Best NHC Proxy (Erin): 00Z ECMWF/CMC/ECENS and 06Z GEFS/12Z GFS
(Dorian)D3: 00Z ECMWF/ECENS and 12Z GFS

For the tropical systems:
   The best proxy for Erin only excludes the UKMET and NAM, as the
remaining guidance is very close to the track and similar in QPF,
which will gradually wind down across Eastern New England tonight
into Thursday.
   The best proxy for Dorian includes the ECMWF and its ensemble
mean, as well as the new 12Z GFS which shifted southwest from its
previous run and is in very close agreement to both the NHC track
and the ECMWF/ECENS. Dorian preferences don't begin until day 3
when it enters the forecast domain.

Rest of the CONUS:
    The guidance continues to feature generally very good
agreement in a SW ridge weakening to become a more broad west-east
flat ridge across the Southern tier. In this flow, there is likely
to be weak impulses and MCS potential across the middle of the
nation, as well as cold front being drive across the northern
tier. These fronts will be pushes eastward by pieces of shortwave
energy shedding around a large Hudson Bay upper low. Outside of
the Canadian which lowers heights too quickly and too drastically
in New England compared to the remaining suite, the global
consensus features little variability in the evolution of the
longwave pattern. For the smaller impulses in the middle of the
country, there remains considerable latitudinal QPF spread among
the various members. This is expected due to difficulty in
resolving small scale features on synoptic time/space scales.
However, the CMC is also a (and the only) clear outlier here with
both the magnitude of QPF and its southern push of MCS features.
For this reason it is excluded from the blend, which otherwise can
include equal weighting of all available global models and
ensemble means. 

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

Weiss