Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1245 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 NAM/GFS Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Long wave trough tracking the Plains Thu closes off over the TN
Valley Sat before
moving to central PA Sun...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 18Z 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 remains close
to the 12Z ECMWF and 12Z ECMWF Ensemble positions as it tracks
into the eastern OH, closer to the model consensus.

The greater model spread with this system occurs with the track of
the surface low. Because it is west of the consensus, the 00Z NAM
surface low position is west of the much of the guidance over
KY/OH. The 00Z GFS has a similar solution to that of the 12Z ECMWF
toward 12Z Sun. However, the consistency of these solutions with
the placement of the surface low over the eastern OH Valley has
been poor. Therefore, a blend of the the ECMWF ensemble mean and
the GEFS mean is preferred, as these solutions have shown better
consistency than the operational runs.


...Short wave crossing the Pacific Northwest and Northern Rockies
Fri and Sat...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non CMC 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. Only the
12Z CMC (too fast with with both short waves) is not in line with
the tightly clustered consensus, so it was not included in the
preference.


...Long wave trough crossing the Baja Peninsula Fri/Sat...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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