Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1247 PM EDT Thu May 16 2019

Valid May 16/1200 UTC thru May 20/0000 UTC

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

12Z NAM/GFS Evaluation with Preliminary Preferences and Forecast
Confidence
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...Overall Pattern across the CONUS...
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Preference: 00Z ECMWF/UKMET and 12Z NAM
Confidence: Average

The trough over the West Coast today and reaching the Plains by
Monday is the main weather maker for the country through this
three day forecast period. The ridge currently up the Plains
shifts east to the East Coast through Saturday as well. By Sunday
morning, another large trough will be near the West Coast. At the
surface, a CO low will develop in the lee of the Rockies through
tonight before eject to IA/MN through Saturday. This low will be
reinforced by a southern plains low that develops on Saturday and
shifts to the southern Great Lakes Sunday. This results in an
extended precipitation patter for the northern Plains into the
Midwest and down the plains through the Day 2/3 timeframe.

Decent agreement is seen by global models through about 18/12Z
when the 12Z GFS and 00Z CMC strengthen the shortwave moving into
the Midwest more than the 00Z ECMWF/UKMET and 12Z NAM. Excellent
agreement is seen in precip across the north-central CONUS by the
00Z ECMWF/UKMET and 12Z NAM and are preferred as of this time. The
12Z GFS and 00Z CMC are in similar camps for precip, but do stand
out with their stronger Midwest shortwave and are less preferred
at this time.

Timing with the second west coast trough/low reaching the CA/OR
border Saturday night through Sunday has remarkable agreement
among currently available guidance and the resultant precip,
driven by terrain as usual is in excellent agreement. Therefore a
general model blend is preferred there.

The only other place of note is east of the Florida peninsula
where the 12Z NAM remains a stronger outlier with an upper low
tracking north across the Bahamas on Days 2/3 and is not
preferred.


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

Jackson