Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
240 PM EDT Sun May 05 2019

Valid May 05/1200 UTC thru May 09/0000 UTC

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

12Z Model Evaluation with Final Preferences and Confidence
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...Overview of the CONUS through Wednesday...
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Preference: 12Z GFS/12Z ECMWF blend
Confidence: Average

...19Z update...

Changes with the non-ncep 12Z guidance include better agreement
with the latitude of the quasi-stationary front Tuesday into
Wednesday with the previous north 00Z CMC adjusting south but not
to the degree of the 12Z NAM which continues to appear too
aggressive with the southward push of the front. The 12Z CMC did
adjust faster though with the surface low in the Great Plains,
again, not to the degree of the 12Z NAM but enough to discount it
as a faster outlier given ensemble clustering back toward the 12Z
GFS and relatively unchanged 12Z ECMWF.

...previous discussion follows...

Broad upper level troughing across the northern U.S. associated
with a northern stream jet will largely stay in place through
Wednesday but amplification of the northern stream will occur
toward mid-week as strong ridging takes shape offshore of the
Pacific Northwest. This will allow phasing with the southern
stream which will carry a closed low into the Southwest Monday and
Tuesday.

At the surface, an area of low pressure and related cold front
will exit the east coast tonight with the focus then shifting
toward the center of the country with a strong cold front settling
into the central Plains and becoming quasi-stationary for Monday
and Tuesday. There are some latitude differences with this front
with the 12Z NAM farther south and 00Z CMC toward the north end of
the spread. The middle ground has been and continues to be
supported by the ensemble means and near a blend of the 12Z GFS
and 00Z ECMWF. Regarding the eventual ejection of lower heights
into the central Plains for Wednesday and associated cyclogenesis,
The 12Z NAM is significant faster than the remaining available
guidance while relative good agreement exists outside of the NAM.
The 12Z UKMET is stronger with the surface low but position does
not appear to differ much from the remaining model consensus.

Therefore, overall, while many of the models have utility at times
across portions of the nation, there is a breakdown at some point
in time for a section of the U.S. Therefore, a blend of the 12Z
GFS and 00Z ECMWF fit with the preferred overall thinking from
coast to coast with the 12Z NAM perhaps the least likely to verify
overall.

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

Otto