Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
308 AM EDT Sat Aug 10 2019

Valid Aug 10/0000 UTC thru Aug 13/1200 UTC

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

00Z Final Model Evaluation with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Days 1-2: General model blend with limited weight on
the NAM
            Day 3: General model blend with limited weight on the
CMC
Confidence: Average, Slightly below average by day 3

07Z Update: Although the general synoptic pattern evolution
remains in good agreement, the 00Z suite has shown an increase in
spread of small scale features both D1-2, and on D3 as well. For
D1-2, through Sunday, the NAM is now a very slow and south outlier
with a potent shortwave ejecting atop Sonora, Mexico and around
the Monsoon ridge towards CO by day 2. Since this feature will
likely aid in producing significant Monsoon rainfall, suggest a
minimal weight on the NAM due to its much different evolution from
the global consensus. By day 3 the CMC remains fast with
shortwaves moving through the more zonal flow.

Previous Discussion:
Flow across the CONUS will gradually transition from a
trough-ridge-trough to a more zonal pattern by early next week.
This flattening of the Central Plains ridge is well agreed upon by
the global suite, and although the NAM is a bit stronger with
lowering the heights across the central CONUS, it is within the
ensemble envelope and can be used in the blend.

The challenge will be how the merging, or at least interaction, of
two shortwaves, one from the filling upper low moving into the Pac
NW, and the other moving into the SW around the Monsoon ridge,
will temporally and spatially evolve into early next week. The CMC
appears the fastest with energy moving atop the ridge in the
increasingly zonal flow, while the UKMET is a bit on the slow end,
especially with its QPF. There remains fairly large spread in the
QPF fields across the Central Plains and into the western Great
Lakes by Monday, despite minimal differences in the position of
the parent shortwaves. Since the CMC begins to outrun the
consensus with this shortwave, as well as with a subsequent
impulse dropping into the NW late on day 3, it should be used with
caution late in the forecast. However, due to the large
variability by day 3, hesitate to remove any of the guidance and
instead recommend just lower weight on the CMC, with significant
use of the means to reduce some of the spread.

  

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

Weiss