Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1251 PM EDT Tue Aug 13 2019 Valid Aug 13/1200 UTC thru Aug 17/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Model Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/00Z ECMWF or near the ECMWF/GEFS ensemble means Confidence: Below Average Zonal flow across the northern tier of the U.S. starts off the pattern, transitioning to a strong ridge in the Southwest and troughing downstream across the eastern half of the nation by Thursday morning. Deamplification of the southwestern ridge occurs by the weekend as mid-upper level troughing moves into the Northwest. While the models agree with the large scale flow, confidence remains lower than average with smaller scale shortwaves within the flow. Across the eastern U.S., differences with an 850 mb low develop on Thursday near the lower Great Lakes/Ohio Valley with the 12Z NAM farthest south and 00Z CMC farthest north. The ensemble means split the difference but with the GEFS mean south of the ECMWF mean. Trends at 500 mb in the ensembles have generally been shifting south across the eastern U.S. over their past 4 cycles, so near the ensemble means but toward the south side seems best. This favorable position is near the 00Z ECMWF/12Z GFS. The 00Z UKMET stands out as a flatter/weaker northern outlier across the East. Across the western U.S., significant trends toward less troughing across the West Coast were observed valid Friday morning. Differences in the deterministic guidance lie more with timing than amplitude. A blend of the 12Z GFS and 00Z ECMWF is preferred for now given their representation lying in the middle of the latest spread. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Otto