Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 AM EDT Wed Jul 15 2020 Valid Jul 15/0000 UTC thru Jul 18/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Longwave trough axis moving through the north-central U.S. through Wednesday with accompanying surface cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/00Z ECMWF blend Confidence: Average As a large closed low and associated longwave trough axis track eastward across southern Canada through the rest of the week, a corresponding cold front will move into the Great Lakes and Great Plains. The 00Z NAM develops convection with a more robust response aloft across the Central Plains that translates eastward toward the Great Lakes region by Thursday morning. The stronger 00Z NAM does not match well with the ensemble means, spaghetti plots and the preferred 00Z GFS/ECMWF. The 00Z UKMET is also a little slower but not as strong as the 00Z NAM. The 00Z CMC could be a secondary option to the 00Z GFS/ECMWF as the Canadian model is the next most similar piece of guidance to the preference. However, both the 00Z UKMET/CMC are stronger with the mid-level ridge in place over the central to southeastern U.S. when compared to the remaining guidance. ...Cut off low west of California by Thursday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models from 00Z are in good agreement, showing the formation of a closed low just west of CA today, and its slow westward translation through the end of the week into the open Pacific. Only minor timing/placement differences were noted, but they are small enough that a general model blend can be used for this system. ...Progressive trough crossing the Pacific Northwest on Thursday, south-central Canada by Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z NAM blend, led by 00Z GFS/ECMWF Confidence: Average The 00Z NAM was noted to be significantly slower with the eastward translation of a mid-level trough axis through the Northwest into the north-central U.S. Friday into Saturday. The differences at the surface across the U.S. are relatively minor, but given the differences in the NAM aloft, it is not recommended to be used for this portion of the country. The 00Z UKMET/CMC show better timing aloft but have differences when compared to the ensemble means and 00Z GFS/ECMWF regarding their greater amplification of the 850-700 mb trough reflection across southern Manitoba/southwest Ontario Friday night. 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 Otto