Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1234 AM EDT Sat Jul 18 2020 Valid Jul 18/0000 UTC thru Jul 21/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Preliminary Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Average Northern tier of the CONUS will remain active with fast flow atop an expansive mid-level ridge covering much of the lower 48. Within the flow atop the ridge, the primary concern is a mid-level shortwave driving a cold front across the country from the Northern Plains this morning, to off the New England coast Tuesday morning. Along this front, a wave of low pressure is also likely to develop and move northeast through the Great Lakes Sunday. Guidance is in very good agreement with the placement and intensity of most feature through the first 48-60 hours. Thereafter, some spread begins to develop with a shortwave progged to drop out of the Northern Rockies Monday morning and then become convectively enhanced late Monday into the Central Plains. As this occurs, it may enhanced the longwave trough amplitude and begin to break down the ridge. By day 3, timing and intensity of these smaller scale features, especially when convectively enhanced, can be troublesome. The large-scale features are generally well aligned so a general model blend still should be reasonable into D3. However, both the NAM and UKMET suggest some tropical moisture with a weak mid-level wave could be pulled northward towards the Gulf Coast on D3, associated with some stronger troughing into the ridge. At this point these are outliers so should be used with caution, but it appears their solutions are due heavily to the evolution of this aforementioned shortwave, for which large-scale evolution remains well aligned. So for now a general model blend is reasonable, but some lesser weight on the NAM/UKMET may lead to a more compromised solution, especially for the Central Plains and Gulf Coast, by Tuesday. 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 Weiss