Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
246 PM EDT Fri May 18 2018

Valid May 18/1200 UTC thru May 22/0000 UTC

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

12Z model evaluation...with final preferences
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...Broad upper trough and embedded MCVs over the Southeast...
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Preference: General model blend
Confidence: Above average

The model show similarly with this system.


...Upper trough crossing the upper Midwest this weekend...
...Cold front/surface wave crossing the region...
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Preference: General model blend
Confidence: Above average

Differences remain with the 00Z ECMWF/CMC flatter with the base of
the departing trough, resulting in a weaker surface low over
southern Ontario. The model have been fairly consistent from run
to run except the UKMET which has been oscillating between
stronger and weaker. A blend with more weight toward the 12Z
GFS/NAM/UKMET is preferred given better agreement in the ensemble
spaghetti heights for weighting away from the weaker 00Z ECMWF/CMC.

19Z update: The 12Z ECMWF/CMC trended close enough to the 12Z
NAM/GFS/UKMET to support a general model compromise.


...Large upper trough/closed lows over the West...
...Ejecting east across the central Plains this weekend...
...Crossing the Midwest by Monday...
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Preference: Blend of the 12Z UKMET/12Z GFS
Confidence: Below average

Ensemble spread has decreased from yesterday, but there appears to
be convective feedback in the NAM and much of the global guidance
which is causing problems with the QPF. Trends from the ensembles
support more in the way of a 12Z GFS/12Z UKMET blend with the 00Z
ECMWF farther north with the surface low across the Plains. The
12Z ECMWF and 12Z CMC adjusted toward the 12Z NAM/GFS/ECMWF
through Sunday but the 12Z ECMWF may still be a tad north while
the 12Z CMC becomes much stronger with the mid-level wave/surface
low. The 12Z NAM is a secondary option early on but it tracks the
surface low fastest to the east by late Sunday into Monday.
Confidence remains low due to the convective details influencing
boundary locations. Please see the QPFPFD for details on
precipitation.


...Upper trough digging into the West on Sunday...
...Energy lifting north out of the northern Rockies...
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Preference: General model blend
Confidence: Above average

The models show good agreement with this system through Sunday
night. Ensemble agreement is strong and trends have been small or
toward the consensus so confidence is above average with this
system.


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

Otto