Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1231 AM EDT Tue Aug 11 2020 Valid Aug 11/0000 UTC thru Aug 14/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Longwave troughing over the Northwest to the Northern Plains Tuesday through Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12z ECMWF/18z GEFS Mean Confidence: Slightly above average During Tuesday through Thursday, the model consensus is for a longwave trough to amplify across the Pacific northwest into northern CA. Low amplitude shortwaves eject and move east northeast across the northern Rockies and northern Plains. On Thu night the models shift the trough axis east across the northern Rockies and high Plains. Minor timing differences develop, with the operational GFS faster than other models. As usual, the GEFS mean had slower forward progression than the operational GFS and is preferred, given the GFS bias of moving longwave troughs too quickly. Mid to Upper MS Valley ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of ECMWF/00z GFS Confidence: Average The differences noted were the 12Z UKMET/CMC/00z NAM showed convectively generated vorticity maxima that resulted in potentially spurious closed lows within progressive waves ejecting northeast across the upper MS Valley. The 00z GFS allowed for a less developed and faster moving low, which appears to be a trend on the right direction. Southeast to Mid Atlantic ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of ECMWF/21z SREF Mean Confidence: Slightly Above Average The models show a high amplitude ridge over the western Atlantic that keeps a mid level trough over the eastern Carolinas and Georgia in place or drifting slowly. This results in increased agreement over prior forecasts. With good agreement among the ECMWF and GFS, along with the ensemble means of the 21z SREF/12z ECMWF Mean, and 18z GEFS Mean, a consensus of these solutions would resolve minor timing/amplitude differences. 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 Petersen