Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
109 PM EDT Sat Aug 10 2019

Valid Aug 10/1200 UTC thru Aug 14/0000 UTC

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

12Z Initial Model Evaluation with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: General Model Blend, with less weight on the 00Z CMC
and 12Z NAM
Confidence: Average, Slightly below average by day 3

Overall the models are in fairly decent agreement in terms of mass
fields as the more amplified trough/ridge pattern begins to erode
into zonal flow by mid-week.  Models do however start to diverge a
bit by Day 3 with the mid-level energy and energy north into the
Canadian provinces.

The biggest differences noted were with respect to mid-level
energy riding between the approaching trough in the west and the
amplified ridge across the central CONUS.  The positioning of this
activity will have large implications with respect to QPF.  As
these mid-level waves move around the northern tier of the ridge,
the lowering heights will eventually deamplify the ridge in the
Plains with time. The trough axis across the Pacific Northwest is
slightly faster with the 00Z CMC which has an impact on the
shortwave activity moving across northern Montana toward the Great
Lakes through Day 2 and into the Northeast by Day 3. Given these
differences are farther from the ensemble clustering, felt lesser
weight should be put on this model overall.

The 12 NAM is also showing subtle differences with its mid-level
wave tracking across the central US toward the Great Lakes. The
model illustrates this activity lowering the mid-level heights and
thus flattening the ridge more quickly than the other model
guidance.  In addition, the impulse tracks too far north by Day 3
across the Great Lakes into the Northeast likely due to a
flatter/less amplified trough/closed low across Quebec. 

Based on the 00Z CMC and 12Z NAM differences, feel these two
pieces of guidance should have less weight within the model blend.
This is also supported by the QPF variability noted among the
models as well.  

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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