Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Thu Sep 06 2018

Valid Sep 06/0000 UTC thru Sep 09/1200 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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...Tropical Depression Gordon...
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Preference: Blend of 05/12Z ECMWF, 05/12Z UKMET, 00Z GFS
Confidence: Slightly below average

07z Update:
00Z Non-NCEP suite has jumped east/north and faster with T.D.
Gordon, likely due to a faster and sharper evolution of the
shortwave moving through the Great Plains. While this is somewhat
supported by some 00Z GEFS solutions and therefore the GEFS mean,
the preferred blend will remain unchanged at this time. However,
this significantly reduces confidence given this large shift and
increased spread from the 00z NAM/GFS and prior runs.  So, the
preference remains unchanged (05/*12z* EC/UKMET and 00Z GFS) with
confidence to slightly below average both in the evolution of
Gordon as well as its associated QPF max placement.

--- Prior Discussion --- 
Overall mass fields are in reasonable agreement across the CONUS
through 12Z/9th. Differences arise with the evolution of T.D.
Gordon across Arkansas into the Mid-Mississippi Valley and its
interaction with a frontal zone. The 12Z CMC is a fast outlier
with its ejection of Gordon to the northeast. Both the 00Z NAM and
GFS trended southward and slower with Gordon, but not
significantly enough to alter the maximum QPF axis or to remove
them from the consensus forecast. A general model blend minus the
CMC is suggested for Gordon with more weight put on the 00Z
GFS/12Z ECMWF/12 UKMET.


...Remainder of CONUS...
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Preference: Non-NAM blend
Confidence: Average

07Z Update:
00Z Suite remains in reasonable agreement for the system moving
into the Pacific northwest. No changes to the non-NAM preferred
blend are needed.

--- Prior Discussion ---
Across the Pacific, an upper low will dig into the Gulf of Alaska
by 00Z/8th, replacing a previous trough which will eject into the
northwest CONUS and get sheared off to the northeast. Strength and
speed differences exist with the evolution of this feature as it
interacts with the terrain of the Rockies. The NAM appears too
strong and then slow with the ejecting shortwave which causes
cyclogenesis well south of the other guidance envelope. The other
models feature subtle differences which manifest into only
moderate spread, and as such the preference is a non-NAM blend
with average confidence. The remainder of the CONUS mass fields
look good enough for a general model blend.


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

Weiss/Gallina