Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1216 AM EDT Thu Aug 6 2020 Valid Aug 6/0000 UTC thru Aug 9/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overall weather pattern across the continental U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Saturday, then 12Z ECMWF/CMC/00Z GFS blend Confidence: Average A moderately amplified upper level pattern exists across the continental U.S. with a western U.S. trough, broad ridge axis across the Plains, and another longwave trough across the Great Lakes and Ohio Valley Thursday morning. Over the next few days, the upper ridge is expected to build further across the southern Plains, and the ridge north of Bermuda also holds strong through the end of the week. Although the closed low initially over Quebec will lift northeast across Newfoundland, a broad trough axis will continue across the Appalachians with slow eastward progress. Across the Pacific Northwest, a shortwave pivoting around the trough is expected to become negatively tilted across southwest Canada and then evolve into a closed low by Friday evening, and a broad positively tilted trough axis across California and Nevada. The models are generally in very good agreement through Friday evening across the continental U.S. and adjacent areas, so a general model blend can be preferred through that time. By Saturday morning, the 12Z UKMET appears too fast in pivoting the developing upper low across south-central Canada, and the NAM flatter with the downstream ridge across Manitoba and Ontario, and slower with the trough crossing the Appalachians through Sunday morning. By the end of the forecast period Sunday morning, the GFS is a little stronger with the trough across the Pacific Northwest and the northern Rockies, and the ECMWF on the weaker side of the guidance. Taking these factors into account, a blend of the ECMWF/CMC/GFS should resolve some of these differences and represent a decent starting point in the forecast process. 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 Hamrick