Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
250 PM EDT Fri Aug 24 2018

Valid Aug 24/1200 UTC thru Aug 28/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Synoptic Pattern across the CONUS...
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Preference: General model blend, with less weight given to the 12z
NAM across the northern Rockies/High Plains Mon
Confidence: Slightly Above Average

For most of the larger scale systems, a general model compromise
among the GFS/UKMET/ECMWF may be applied.  Good agreement remains
with the deamplification of the upper trough currently in the
upper MS Valley as it crosses the Great Lakes and then into
southeast Canada.

The models persist in showing development of a western US trough,
with a pair of 700 mb waves.  The first wave comes out across the
northern Plains, with phasing differences developing on Monday
resulting in differences on where low pressure develops along the
surface from from the the central Plains to the upper MS Valley.

Aloft, the NAM has lower 700-500 mb heights in ND vs the
GFS/ECMWF/UKMET.
Otherwise, there is good timing agreement with the trough, except
the 12z ECMWF is faster with the 500 mb trough movement. 
Confidence is lower in the 12z ECMWF trends given the 00z Mean and
operational 00z ECMWF clustered better with frontal timing
compared to each other and the 12z UKMET/GFS/NAM.

Better agreement exists with the trough as it exits the Pacific
northwest and crosses the northern Rockies Sat night and then
again as a secondary wave develops and moves into the base of the
trough on Monday as the trough moves out of ID into WY and eastern
MT.

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

Petersen