Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
315 AM EDT Thu Apr 18 2019

Valid Apr 18/0000 UTC thru Apr 21/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
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...Long wave trough tracking across the Plains Thu closes off over
the TN Valley Sat before
moving to western PA Sun...
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Preference: Blend of the 00Z GEFS Mean/12Z ECMWF ensemble mean
Confidence: Average

The 00Z NAM/GFS are close to the consensus with the long wave
trough as it amplifies over the Southern Plains Thu, before
closing off over the TN Valley during Fri. After that time, the
00Z NAM appears to dig too much short wave energy into the back of
the long wave trough, resulting in a slower progression of the
closed low into the eastern OH Valley. The 00Z GFS was much
broader with the mid level system, while the 00Z operational ECMWF
was further west with its depiction of the closed mid level low
over WV, but was still within the 00Z model consensus.

The greater model spread with this system occurs with the track of
the surface low. The 00Z ECMWF/12Z ECMWF ensemble mean were
further northeast with the surface low, with a position over
western PA (which was close to the 00Z NAM position at 19/12z).
The 00Z GFS/00Z GEFS mean solutions have a surface low at that
time over western OH (close to the 00Z UKMET solution).  Given
that there could be two or even three surface lows or
redevelopments in this area on Sat, the spread is not surprising.
Since the operational runs continue to show a large amount of
spread, a blend of the ensemble means is the preferred solution
with this system.


...Short wave crossing the Pacific Northwest and Northern Rockies
Fri and Sat...
,,,Short wave energy crossing northern CA Sat...
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Preference: 00Z ECMWF/GFS/NAM blend.
Confidence: Slightly above average

Both the 00Z NAM and 00Z GFS were close to the consensus with the
initial short wave crossing the Pacific Northwest and Northern
Rockies Fri into Sat before it weakens, as well as the next short
wave in the flow as it crosses northern CA Sat into Sun.

By contrast, the 00Z CMC remains faster with both short waves, and
the 00Z UKMET slows as it closes off a mid level center over
western NV. Since these two model do not fit the tightly clustered
solution offered by the 00Z ECMWF/GFS/NAM, they were omitted from
the preferred solution.


...Long wave trough crossing the Baja Peninsula Fri/Sat...
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Preference: General model blend
Confidence: Above average

The 00Z NAM/GFS clustered closely with the other guidance bringing
the short wave remnants of the closed mid level low west of the
Baja Peninsula across this area Fri into Sat. Because of this, a
general model blend is preferred, with above average confidence. 

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

Hayes