Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
236 AM EDT Mon Apr 30 2018

Valid Apr 30/0000 UTC thru May 03/1200 UTC

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

00Z model evaluation...with final preferences
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...Closed low moving through the Northeast today with associated
surface low...
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Preference: General model blend
Confidence: Above average

The models show similarly with this system.


...Upper level trough over the Intermountain West today, with
resulting shortwaves ejecting northeast into the Northern Plains
through Tuesday...
...Lee cyclogenesis over the Plains with a surface low pushing
through the Upper Midwest and into Ontario Tuesday into
Wednesday...
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Preference: 00Z NAM, 00Z GFS, 00Z ECMWF blend
Confidence: Slightly below average

As a mid-level shortwave trough ejects out into the central and
northern Plains on Monday/Monday night, it is expected to
deamplify, breaking down into a few smaller scale vorticity
maxima/ripples in southwest flow. At the surface, a low will track
through Minnesota Tuesday morning. The 00Z GFS is on the northern
side of the ensemble and deterministic spread and becomes a bit
weaker through the day on Tuesday. However, aloft, it is a
reasonable fit with the 00Z ECMWF and 00Z NAM. While the 00Z CMC
trended toward the consensus and is no longer an outlier with it
surface low, the CMC still lies south of the better model
agreement. The cold front extending south from the surface low
that tracks into Ontario early Wednesday is faster in the 00Z GFS,
partly due to its alternative handling of the surface low track
with better support for a slower boundary, nearer to the 00Z NAM
and 00Z ECMWF. However, given each of the three models when
blended together allows for a reasonable placement given the
ensemble spread, a 00Z NAM, 00Z GFS and 00Z ECMWF blend is
recommended.

Please note the above preference reflects mass fields, and not
QPF/convective details which can be found in the WPC QPF
discussion (QPFPFD).


...Shortwave digging southward off of the West Coast today, with a
low possibly closing off aloft by Wednesday morning in the
Southwest...
...New surface low development in the central High Plains...
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Preference: General model compromise
Confidence: Slightly below average

Ensemble spaghetti heights do not favor the slower 12Z UKMET/CMC
as the trough begins to eject into the Plains, so the speeding up
observed in the 00Z UKMET/CMC appears to be a good move. While the
00Z NAM/00Z ECMWF show good agreement with the resulting surface
low and frontal boundary, ensemble scatter low plots show a wide
range of possibilities, with the 00Z GFS/UKMET/CMC within the
spread, although THEY ARE displaced farther north and west valid
12Z/03 over Kansas. A general blend is preferred at this time, but
with reduced confidence in the exact details.


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

Otto