Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
235 AM EDT Tue Sep 04 2018

Valid Sep 04/0000 UTC thru Sep 07/1200 UTC

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

00Z model evaluation...with latest preferences and confidence 
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...Overall Synoptic Pattern across the CONUS...
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Preference: Blend of the 00Z GFS and 00Z ECMWF
Confidence: Average 
 
The strong subtropical ridge over much of the Eastern U.S. will
remain in place going through Wednesday, but should begin to break
down on Thursday as a shortwave trough over southern Canada
advances east toward the Great Lakes and Northeast by Thursday.
This will ultimately drive a cold front across the Midwest, Great
Lakes and then down across the Northeast and Mid-Atlantic by the
end of the period. The 00Z NAM is the one model that sticks out as
a deeper outlier with this shortwave energy and will be discounted
given good global model agreement seen otherwise.

Meanwhile, the mean layer upper trough over the Northwest U.S.
should tend to remain intact through Tuesday, but this energy will
be lifting out and shifting eastward across southern Canada
through Wednesday. In its place will be a building shortwave ridge
as deeper height falls evolve farther offshore of the Pacific
Northwest. The 00Z CMC is the slowest solution overall with this
offshore trough, with the 00Z NAM/GFS/UKMET/ECMWF solutions better
clustered on a somewhat more progressive solution, and this latter
cluster has better ensemble support from the GEFS mean and ECENS
mean. Elsewhere, the weak trough over the Four Corners region will
tend to weaken further as heights regionally begin to come up a
bit, but the guidance agrees in maintaining at least a mid level
shear axis/trough across the immediate central and southern High
Plains. The 00Z ECMWF is a bit farther west with this trough axis
compared to the model consensus. The 00Z UKMET meanwhile is the
weakest solution. Based on the latest model clustering and trends,
a blend of the 00Z GFS and 00Z ECMWF will be preferred across the
CONUS.


...Tropical Storm Gordon...
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Preference: Please consult the latest NHC forecast track
 
Tropical Storm Gordon is forecast to move west-northwest and
approach the central Gulf Coast late Tuesday or Tuesday night.
Thereafter, the system will continue inland across the lower MS
Valley as it tracks around the southwest periphery of the strong
subtropical ridge over the Eastern U.S. The latest global model
consensus is in very good agreement on the track heading which is
in the vicinity of far southeast LA or southern MS by 00Z
Wednesday. The 03Z NHC forecast track is overall a bit to the
right of the global model consensus, although appearing to be
closest to a blend of the 00Z GFS and 00Z ECMWF through 72 hours.
In time, the 00Z NAM becomes the farthest south and slowest
solution as the system approaches and the central Gulf Coast and
then moves inland. The 00Z UKMET also tracks Gordon a bit south of
the model consensus after landfall. Please consult the latest NHC
public advisories and discussions for more information on this
system.


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

Orrison