Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
101 PM EDT Wed Oct 03 2018

Valid Oct 03/1200 UTC thru Oct 07/0000 UTC

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

12Z NAM/GFS Evaluation...with Preliminary Preferences and
Confidence
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...Overall Pattern Across the CONUS...
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Preference: non 12Z NAM blend
Confidence: Slightly above average

This morning's upper air pattern over the lower 48 showed a large
ridge over the south-central and southeastern U.S. with a closed
low just west of California and a progressive and compact
shortwave moving east across the north-central U.S. The shortwave
over the north central U.S. will aid in the amplification of a
deepening surface cyclone to track into Ontario and Quebec with a
trailing cold front sweeping through the Great Lakes and Northeast
tonight through Thursday night. Meanwhile, the closed low off of
the California coast will weaken as it tracks north of the
Southeast ridge into the Great Lakes region Thursday night, and
will be followed by a couple of shortwaves into the western U.S.
The end result by Saturday will be an amplified pattern over the
lower 48 with troughing over the West and ridging over the East.

The overall differences in mass fields were not large, but the 12Z
NAM was noted to be colder with thermals across the northern Great
Basin and northern Rockies compared to the remaining deterministic
guidance. This is a typical NAM bias and will not be favored.
Elsewhere, the 12Z GFS was noted to be a bit more progressive with
overall upper trough progression into the Plains, but was similar
to the non 12Z NAM consensus of guidance with low placement and
frontal timing east of the Rockies. Overall, a non-12Z NAM blend
is recommended across the lower 48 through Saturday.

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

Otto