Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 249 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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Preference for the Entire CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Proxy for Rosa: 12z ECMWF/UKMET Confidence: Slightly above average 19z Update: No major differences noted in the 12z ECMWF/UKMET/CMC with regard to the longwave trough and flow over the central US through the weekend. With respect to Rosa, the eastward shift in the UKMET/ECMWF aligns more with the official NHC track and suggests that a blend of the two would be a better proxy at this time. ---Previous Discussion--- 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