Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1252 PM EDT Sun Apr 15 2018

Valid Apr 15/1200 UTC thru Apr 19/0000 UTC

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

12Z NAM/GFS evaluation and preliminary preferences
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...Midwest cyclone becoming centered over New England by
Wednesday...
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Preference: General model blend
Confidence: Slightly Above Average

The models have converged on the upper level evolution of the
cyclone currently over Ohio valley as it tracks east. Only minor
strength/position differences remain with the upper and lower
level evolution such that a general model blend can be used to
iron out any remaining differences.


...Trough progressing Through the West, Reaching the Plains late
Tuesday...
...Surface low tracking from KS into the Ohio valley/Great Lakes
through late Wednesday...
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Preference: Blend of the 00Z ECMWF/UKMET
Confidence: Average

Ensemble spaghetti height trends showed that the faster members
along with the faster NAM, GFS and CMC from Saturday have all
trended slower for today's runs, while the slower members have
generally stayed the same over the past 3-4 cycles. The ECMWF mean
continues to look like a favorable middle ground considering
convergence in ensemble guidance...which splits the difference
between the slightly faster 00Z UKMET and slower 00Z ECMWF. The
12Z NAM and GFS continue to appear too fast lying toward the east
end of the ensemble spread through Tuesday night across the middle
of the country. The centroid of ensemble scatter low plots also
agrees well with a 00Z ECMWF/UKMET blend.


...Next Pacific trough reaching the West Coast Tuesday night...
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Preference: non 00Z UKMET blend
Confidence: Average

On Wednesday, another trough axis is expected to near the West
Coast with ensemble spaghetti plots showing a modest degree of
possibilities. The slower GEFS/GFS has trended closer to the
middle, but the 12Z GFS and 12Z NAM are toward the faster/southern
side with the base of the trough, while the 00Z ECMWF/CMC are
slower/less amplified to the north valid 00Z/19. Only the 00Z
UKMET differs significantly here and has only a strong minority of
ensemble support with its faster/less amplified trough
progression.. Therefore, a blend of the GFS/ECMWF idea should work
well here, with the NAM supporting the GFS and CMC supporting the
ECMWF.

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

Otto