Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1257 AM EDT Wed May 29 2019

Valid May 29/0000 UTC thru Jun 01/1200 UTC

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

00Z Model Evaluation Including Preferences and Forecast
Confidence...
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...CONUS from Rockies eastward...
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Preference: Non-CMC blend through 30.12z
            ECMWF/GFS/UKMET blend after 30.12z 
Confidence: Average to slightly below average

A pattern change will evolve over the CONUS through the next 3
days as a closed low over western Nebraska emerges into the
central Plains and eventually reach the Ohio Valley by Thursday
night. By this weekend, it will interact with a stronger closed
low over James Bay and force large scale troughing over the Great
Lakes and eastern US. Meanwhile, out west there will be a weak but
persistent closed low over southern California. The biggest model
differences lie on day 2/3 as a couple of shortwaves round the
base of the developing trough.

The closed low energy gradually weakens and opens up over the
Midwest and then gets kicked east as it phases with the large low
over James Bay. How quickly this happens is a model difference,
with fairly good agreement in the GFS/ECMWF/UKMET through 48
hours. The NAM is too slow while the CMC holds back the energy all
the way toward Nebraska, which seems unrealistic. As it swings
through the mid-Atlantic on Friday, the NAM/GFS are fast while the
ECMWF/UKMET are on the slower end.


...West Coast/Great Basin...
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Preference: General model blend
Confidence: Slightly above average

In the West, with the shortwave accelerating around the base of
the trough, a very weak ill-defined trough/flow remains upstream
positive tilt ridging into the far Pacific Northwest by Thursday
allows for broad but weak closed low/trof to develop over
California by Friday.  Guidance, there is solid model agreement
here with the evolution/timing and placement to have confidence in
a general model blend at slightly above average confidence.

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

Taylor