Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1220 AM EDT Wed Apr 17 2019

Valid Apr 17/0000 UTC thru Apr 20/1200 UTC

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

00Z NAM/GFS Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General Model Blend through Day 2, 12Z ECMWF
Ensemble/18Z GEFS mean Day 3
Confidence: Slightly Above Average through Day 2, Average on Day 3

The main system for the CONUS for this period is the evolving long
wave through tracking across the Southwest and Southern Plains,
before closing off across the TN/OH Valleys during Day 3. Through
Day 2, both the 00Z NAM and 00Z GFS are close to the consensus as
the system elongates into a full latitude trough stretching from
the Upper Great Lakes into the Lower MS Valley. These solutions
are also close to the consensus developing a secondary surface low
on the front and taking into the into lower OH Valley. Based on
the relatively good agreement, forecast confidence is slightly
above average.

After that time, the 00Z NAM (and to some extent the 00Z GFS) slow
the progress of the long wave trough, before it closes off over
the lower OH Valley by the end of Day 3. The 12Z ECMWF ensemble
mean and the 18Z GEFS mean are closer with the mid level system as
both close it off over eastern
KY/southwest WV. This compromise position is closest to the 00Z
NAM/00Z GFS by 20/00Z, but thereafter the spread in the position
of the secondary low increases greatly. Because of the spread,
forecast confidence is only average (at best).

Model solutions are speeding up the timing of short wave energy
crossing the Pacific Northwest and Northern Rockies through Day 3,
which is reasonable given the speed of the mid level flow
upstream. There is enough model agreement here to recommended a
general model blend with slightly above average confidence.

Finally, there is good model agreement with the closed mid level
low well east of the northern Baja Peninsula on Day 2 as it
weakens and crosses the peninsula during Day 3. Because of this, a
general model blend should suffice.


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

Hayes