Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 225 PM EDT Mon Jul 27 2020 Valid Jul 27/1200 UTC thru Jul 31/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-upper level troughing over the Great Lakes and Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models have remained consistent in showing a closed low dropping southeast across Ontario on Monday and Tuesday before drifting east across Quebec on Wednesday and Thursday. Meanwhile, a larger scale trough is shown deepening and moving east across the Great Lakes into the Northeast -- driving a well-defined surface cold front through the region. Overall, models are in good agreement with the larger scale pattern through late Thursday. ...Mid-level energy over California/Great Basin... ...Energy advancing southeast across the Plains by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend through 72 hours, followed by a solution more similar to the NAM/ECMWF the central Plains Confidence: Average Models continue to the show the mid-level energy that is currently over California lifting to the northeast into the northern Intermountain Region and Rockies Monday and Tuesday, before dropping southeast into the High Plains along the eastern periphery of an amplifying ridge centered over the Southwest and Great Basin. Models continue to show some timing differences, especially late in the period with a well-defined shortwave that is forecast to settle into the central Plains on Thursday. While most models have trended faster with this feature, including the 12Z ECMWF, consensus suggests the GFS is too fast dropping this system south through the central Plains on Thursday. ...Upper low/trough approaching the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 60 hours, followed by a lean toward the GFS and ECMWF Confidence: Average Models show a deepening upper low settling south from the Gulf of Alaska into the northeastern Pacific. While the strong downstream ridge is expected to keep the low center well offshore, models do show some longitudinal differences late in the period -- with the GFS, ECMWF and their latest ensemble means slightly farther east than the NAM and UKMET. The NAM is also on the southern edge of the envelope guidance with the low center as well. 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 Pereira