Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1253 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 NAM/GFS preferences...with preliminary 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, 12Z 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 12Z ECMWF and 00Z NAM. The 12Z CMC stands
out the greatest with a displaced low relative to the better
ensemble clustering. 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 12Z 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 12Z 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: 00Z NAM, 00Z GFS; 12Z ECMWF blend
Confidence: Slightly below average

Ensemble spaghetti heights do not favor the slower 12Z UKMET/CMC
as the trough begins to eject into the Plains. While the 00Z
NAM/12Z 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 within the spread, although it
is displaced farther north and west valid 12Z/03 over Kansas. A
3-way blend is again preferred at this time, but with reduced
confidence.


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

Otto