Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 230 PM EDT Wed Jul 15 2020 Valid Jul 15/1200 UTC thru Jul 19/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Long wave trough crossing the north central US through Thu with an accompanying surface cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 12Z NAM/GFS are close to the model consensus taking the broad long wave trough from the Upper MS Valley this afternoon into western Quebec Fri morning, though the 12Z GFS might be a bit faster than the consensus at this point. There is also good clustering with the timing of the associated surface cold front, though the 12Z GFS might be a bit faster than the consensus reaching the Northeast Fri afternoon. However, none of the model differences were significant enough to keep them out of the preferred blend. Due to the good clustering, forecast confidence has increased with this model cycle. ...Cut off low west of California by Thursday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Both the 12Z NAM/GFS are close to the model consensus with the development of a closed mid level low just off the southwestern CA coast late Thu into early Fri. They are also close with taking the mid level system west into the Pacific with time. Since placement and timing differences are fairly minor, a general model blend is preferred with this system. ...Long wave trough crossing the Pacific Northwest Thu, moving into south central Canada by Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z NAM blend Confidence: Average There is generally model model clustering with the long wave trough that crosses the Pacific Northwest Thu morning. As the trough moves into Manitoba/Saskatchewan Sat into Sun, model spread develops with respect to timing. While all of the most recent model solutions slow the trough as it reaches central Canada, the 12Z NAM continues it's model trend of being slower than the consensus, especially by 12z Sun. A cold front associated with the trough extends from the Upper MS Valley into the Central Plains by that time. The 12Z non-NCEP guidance (especially the 12Z UKMET/ECMWF) slowed their timing of the front from WI into NE during Sat, suggesting that the 12Z NAM is not as much of an outlier. However, since the 12Z NAM is still slow with the trough across central Canada, it remains out of the forecast preference. 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 Hayes