Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
103 PM EDT Wed Jul 31 2019

Valid Jul 31/1200 UTC thru Aug 04/0000 UTC

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

12Z Preliminary Model Evaluation and Preferences/Confidence
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...Overview of the CONUS features...
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Preference: Non-UKMET through day 2
    ECENS/GEFS/NAEFS mean day 3
Confidence: Above Average through day 2
            Below Average day 3


Guidance is in very good agreement through day 2 with a persistent
Monsoon ridge centered over New Mexico on day 1 shifting slowly
westward with time through day 2 into the weekend. Downstream of
this feature, broad longwave troughing will exist across the
eastern half of the CONUS. Significant shortwaves lifting onto the
PacNW coast day 2 and approaching Northern New England on day 3
will generally remain north of the international border with
Canada. More significant but smaller-scale impulses will rotate
around the Monsoon ridge through the period bringing rounds of
thunderstorms and potential MCS's from the Southwest through the
Central Plains and into the Mississippi Valley.

The UKMET continues to be a strong outlier with its ridge strength
noted by heights that are generally 2-4dm higher than the global
consensus across the west. This has been a trend in the UKMET
recently. Additionally, the UKMET is quick to spin up weak
impulses in the Gulf of Mexico into two stronger closed features
with surface reflection, which is not echoed by any other model.
For these important reasons the UKMET is discounted from the blend.

By day 3, the guidance splits considerably with an important
feature dropping around the periphery of the ridge into the
Central Plains and Mid-Mississippi Valley. The GFS/NAM drive this
feature much further SW both in vorticity fields and QPF, while
the Non-NCEP guidance keeps the feature much further north. The
separation is significant, several degrees latitude, and at this
time there is no clear preferred solution. However, the
shortwave/MCS on day 2 may break down the ridge enough to support
the further south NCEP solution, lending some credence to the
NAM/GFS. Due to the considerable spread in the deterministic
guidance, and a much smaller spatial envelope in the means, think
an ensemble approach is best for now with the NAEFS lying
somewhere in between the ECENS and GEFS mean.


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

Weiss