Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1247 PM EDT Sat Jul 11 2020 Valid Jul 11/1200 UTC thru Jul 15/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation with Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave crossing the Northeast through Sun... ...Associated cold front crossing the Great Lakes... Preference: 00z ECMWF/12z GFS/NAM model blend Confidence: Average The models show a 700 mb trough moving slowly across the northeast tonight through Sunday, driving a cold front across NY/New England. The prior runs of the UKMET had a high amplitude 700 mb trough but the 12z run has backed off on the trough amplitude and the strength of sfc low pressure across the border in southeast Canada. Given good and improving clustering of solutions, a multi-model blend will work well for this system. ...Mid-level shortwave to cross the Mid-Upper MS Valley tonight, Ohio Valley Sunday, Great Lakes to the Appalachians/northern mid Atlantic/NY/New England Monday... Preference: Blend of 12z GFS/00Z UKMET/00Z CMC/00Z ECMWF mean/06Z GEFS mean Confidence: Average The models now have better agreement with the timing of the 700-500 mb trough as it crosses the OH Valley. The 12Z NAM is a few hours faster, with 09z SREF Mean and 06z GEFS Mean clustering well with the GFS/UKMET/ECMWF. The 12z GFS is not as amplified as other models/06z GEFS Mean. Once the mid level trough moves east of the central Appalachians, low pressure may develop along the front as it crosses NJ/southern NY/New England. Typical rimming differences exist among the UKMET/ECMWF/NAM, with the UKMET slowest of all. A blend of the 00z ECMWF/09 SREF Mean/00z ECMWF Ensemble Mean/00z UKMET/12z NAM could be used to mitigate the differences. ...Longwave trough axis moving into western Canada and the northwestern U.S. on Sun... Preference: Blend of 00z ECMWF/12z UKMET/12z NAM Confidence: Slightly Above Average The models show a broad 500 mb trough and associated surface cold front moving across the Pacific Northwest and Northern Rockies Sunday to Sunday Night and Northern Plains Monday. Mainly minor timing differences were noted in the latest guidance, with the 12z GFS a few hours faster with the mid level trough than the NAM/UKMET/ECMWF/Canadian global. Given the long history of a fast bias in the GFS with longwave troughs, and blend of the other solutions is preferred. There is a possibility of a secondary low amplitude wave moving east from WY/CO across KS/NE on Tuesday, with the NAM a little more amplified than the GFS/ECMWF. Given the confluent flow in the mid-upper jet, a new wave developing is a distinct possibility, so blending equally weighted solutions is preferred until a resolution develops. 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 Petersen