Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1238 PM EDT Thu Sep 27 2018

Valid Sep 27/1200 UTC thru Oct 01/0000 UTC

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

12Z Final Model Evaluation...with Preferences and Forecast
Confidence
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...Overall Preference for the Entire CONUS...
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Preference: General model blend
Confidence: Slightly above average

Longwave troughing across the central US will transition to zonal
flow by this weekend as a Rex block off the West Coast gradually
breaks down allowing energy to stream into the Pacific NW and
northern Rockies. At the surface, a low will track from the Upper
Midwest into Canada with a building high pressure into the
Northern Plains through Saturday. A lingering frontal boundary
across the Gulf Coast region into portions of the Southeast US
will stall out. Overall, the main deterministic and ensemble
guidance are in relatively good agreement with these major
synoptic features with minor sensible weather differences noted. A
general blend of the guidance is preferred.

Across the West Coast and also regarding Rosa, larger differences
in the guidance toward by the end of Day 3 (10.00z). There is
noted spread between tracks and speed with Rosa and another
shortwave trough approaching the West Coast next week. The 27.12z
NAM and GFS were faster than a consensus bringing moisture into
the southwest US associated with Rosa as it moves toward the Baja
of California, with the NAM significantly faster and further from
preference/official NHC forecast. The GFS would also be a bit
faster than the NHC forecast turning north and being east of the
NHC track.  There is quite a bit of uncertainty with the track so
please see the latest NHC statements on Rosa.

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

Taylor