Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1254 AM EDT Sat Oct 20 2018

Valid Oct 20/0000 UTC thru Oct 23/1200 UTC

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

00Z NAM/GFS evaluation...with preliminary preferences and
confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of the 12z ECMWF/UKMET
Confidence: Slightly above average

The synoptic setup from early Saturday morning featured a
quasi-rex block over the western US with downstream troughing over
the central/eastern US. Over the next 24 hours, a shortwave
dropping south from the Ontario/Quebec border will bring a renewed
surge of cold air to the Great Lakes, Ohio Valley and Northeast
extending through Sunday. Another shortwave will reach the Great
Lakes region on Monday. Meanwhile out West, a closed low/upper
trough will slowly track east from the California coast into the
southern Great Basin as upper ridging edges east toward the
Canadian Rockies as upper level troughing nears the Pacific
Northwest.

Some of the greatest differences were across the Great Lakes
region with timing/amplitude of shortwaves. Most notably, this was
with a shortwave over the Great Lakes on Monday where the 00Z GFS
is faster than the consensus and a majority of ensemble guidance,
while a blend of the non 00Z GFS models are reasonable here.

Across the Gulf of Mexico, the 12Z CMC stands out with how it
handles a front/low in the western Gulf compared to the remaining
model guidance, while the 00Z NAM is significantly stronger with
850 mb frontal convergence over southern and eastern Texas which
is likely overdone.

Overall, a blend of the 12Z ECMWF/UKMET is favored across the
entire lower 48.

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

Otto