Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
245 AM EDT Sat May 18 2019

Valid May 18/0000 UTC thru May 21/1200 UTC

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

00Z Model Evaluation with Final Preferences and Forecast Confidence
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...Overall Pattern across the CONUS...
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Preference: 00Z GFS/12Z ECMWF blend
Confidence: Average

...07Z update...

Adjustments made by the 00Z ECMWF/UKMET/CMC compared to their
previous 12Z cycles were greatest across the Pacific Northwest
with the UKMET trending north and CMC south valid 12Z/21. The 00Z
ECMWF also went a little north which affects the closed low
ejecting east across Colorado and New Mexico. Given the tightening
of ensemble spaghetti heights into the Plains, prefer to stay
toward the middle of those ensemble members versus going with the
westward shift back west from the 00Z ECMWF. Run to run
consistency has not been great from the ECMWF

...previous discussion follows...

Three large mid-level troughs will be the main driving factors for
sensible weather across the CONUS through the next 3 days. The
initial trough, currently crossing the central and southern
Rockies, will push into the southern/central Plains today as a
strong surface low tracks through Nebraska early this morning with
weakening tonight in favor of a second low over Kansas to
strengthen by this evening. That low will translate into the Great
Lakes region for Sunday night as another closed low moves through
the Great Basin and a third mid-level closed low starts to
approach the Pacific Northwest. The next trough advances into the
western US Sunday followed quickly by another trough on Monday or
Tuesday.

A 00Z GFS, 12Z ECMWF, 12Z UKMET blend continues to look best for
the first system and surface low reaching the Great Lakes region
on Sunday, with the 00Z NAM a bit faster and 12Z CMC slower
(located on the edge of the latest ensemble spread). The second
trough axis has had poorer run to run continuity but ensemble
spread has decreased with the timing compared to previous days.
While trends faster/slower will still be possible, a middle ground
is recommended, closest to the middle of the SREF/GEFS/ECENS means
and best represented by a 12Z ECMWF/00Z GFS blend. The 00Z NAM is
a close second option while the 12Z UKMET and CMC are slower for
system number two, more notably in the 12Z UKMET which is a slow
outlier. For the third trough to near the Pacific Northwest Monday
night, the 00Z GFS/12Z ECMWF are closest again to the ensemble
means and are in the middle of the deterministic spread. A general
model blend is preferred for smaller scale systems not referenced
above.

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

Otto