Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Sat Aug 8 2020 Valid Aug 8/0000 UTC thru Aug 11/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overall weather pattern across the continental U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Sunday, then ECMWF/GFS/CMC Confidence: Average 7Z Update: The 00Z NAM is slower and considerably stronger with the shortwave crossing the northern Plains and Upper Midwest on Monday compared to all of the other 00Z guidance. The ECMWF trended slightly stronger with the upper ridge across the Midwest and the Ohio Valley and in line with the UKMET. Otherwise, no major changes noted with the arrival of the full 00Z model suite. ---------- The overall weather pattern across the continental U.S. will be quasi-zonal across the northern tier states on Saturday with a building upper ridge centered over the southern Plains region. A weak trough axis over the Mid-Atlantic region and the Northeast U.S. will continue to slowly emerge offshore followed by low amplitude ridging aloft. There will also be a broad, positively tilted trough axis stretched across the Intermountain West and extending across California. The main weather feature will be an evolving closed low over south-central Canada with multiple shortwave perturbations rotating around its southern periphery, and these shortwaves will sustain cold frontal passages across the north-central U.S. through Monday. There is enough deterministic model agreement through 12Z Sunday to merit the use of a general model compromise. Beyond that, the 00Z NAM becomes a bit more amplified with the upper low across Saskatchewan and Manitoba, and slower with the shortwave crossing the northern Plains by Monday. The GFS is more potent with the leading shortwave across the Upper Midwest by Monday morning. The 12Z UKMET is a little stronger with the upper level ridge across the Ohio Valley by the end of the forecast period. Taking these factors into account, using a 12Z ECMWF/GFS/CMC blend as a mass field starting point should work 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 Hamrick