Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1220 PM EDT Sat Jul 18 2020 Valid Jul 18/1200 UTC thru Jul 22/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern tier of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00Z ECMWF Confidence: Slightly above average The northern tier of the CONUS will remain active with fast flow atop an expansive mid-level ridge covering much of the central and southern U.S. A pair of shortwave troughs though will be advancing across the northern Plains and upper Midwest going through early next week, with a shortwave trough also expected to be approaching the Pacific Northwest by late Tuesday. The 00Z CMC appears a bit too slow with the first shortwave crossing the northern Plains and upper Midwest on Sunday. By Tuesday as the next shortwave arrives across this region, the 00Z UKMET appears to be a bit too weak. By late Tuesday with the energy approaching the Pacific Northwest, the 12Z NAM may be a tad too strong and slow with its energy given the good global model clustering seen otherwise. Overall, the preference is toward a blend of the 12Z GFS and 00Z ECMWF across the northern tier of the CONUS given their better clustering with all three shortwave troughs mentioned. ...California/Southwest U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS and 00Z ECMWF Confidence: Average The models advertise a broad mid-level trough along and just offshore of northern/central CA by Monday and Tuesday, with a separate smaller scale shortwave trough developing over areas of the Southwest involving southern NV, southwest CA, western UT and northwest AZ by late Tuesday. The 00Z CMC and 00Z UKMET both are on the weaker side of the global model suite with both systems. The 12Z NAM/GFS and 00Z ECMWF are better clustered with placement and positioning of these troughs, and have better ensemble support from the GEFS/ECENS means. Thus a NAM/GFS and ECMWF blend will be preferred. ...Mid-level easterly waves impacting the southern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00Z ECMWF Confidence: Average A series of mid-level troughs/easterly waves with at least a modest surface reflection will impact the southern tier of the CONUS over the next few days with an emphasis on the Rio Grande Valley, Gulf Coast, and the FL Peninsula. The 12Z NAM is generally a tad too strong it appears with this wave activity as the global models and the ensemble means are all generally flatter with their westward propagation through the period. A non-NAM blend will be preferred with the wave activity as a result across the southern tier of the CONUS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Orrison