Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Fri Aug 09 2019

Valid Aug 09/1200 UTC thru Aug 13/0000 UTC

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

12Z Final Model Evaluation with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General model blend
Confidence: Average

...19Z Update...
The latest models guidance (12Z UKMET/CMC/EC) actually gives a bit
more credence to the 12Z GFS. If anything, the 12Z ECMWF is
showing the slowest progression now with the energy moving through
the Upper Midwest toward the end of Day 3.  Whereas the rest of
the guidance shows a steady progression as the mid-level wave
propagates eastward.  Given this and the subtle difference with
respect to the mid-level impulses, feel a general model blend is
best. 

...Previous Discussion...
Model guidance is in generally good agreement until Day 3 where
variability are most prominent. A trough approaching the west
coast will continue to move inland, meanwhile ridging across the
central CONUS will migrate a bit to the east.  A trough in the
northeast will eventually pivot its mid-level energy offshore. 
The main differences is with respect to mid-level height fields
and the vorticity that follows the gradient.  These features are
very hard to track with any degree of certainty as the mid-levels
become more ambiguous in time. 

The mid-level low moving across northern Saskatchewan, Manitoba
and Ontario will leave a trail of mid-level impulses moving across
the northern tier of the U.S. (from the Rockies into the Great
Lakes region).  Models vary quite a bit with the overall
placement, timing and strength with this feature which is
resulting in impressive differences in QPF on Day 2 and most
notably on Day 3.  While the 12Z GFS has been quite consistent
with the faster solution of the low and resultant mid-level
energy, feel this solution is slightly out of tolerance compared
to the clustering of the other model guidance/ensembles. In
addition, differences are noted with the approaching trough and
the strength of the mid-level low/impulses as energy rides north
interacting with monsoonal moisture. Therefore, putting sightly
less weight on the 12Z GFS across the CONUS.  The difference with
respect to the other model guidance is within the model cluster
with little overall spread.  

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

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