Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1247 PM EDT Wed Apr 8 2020 Valid Apr 8/1200 UTC thru Apr 12/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Initial Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Great Lakes to East Coast trough and low pressure system ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/NAM/00Z ECMWF Confidence: High A closed low initially over Manitoba will continue tracking eastward north of the Great Lakes and reach northern New England by 12Z Friday, with a pair of shortwave perturbations pivoting around it from the Upper Midwest to the East Coast. This will support a strong cold front reaching the East Coast Thursday afternoon and a big surface low near Maine by Friday morning. The overall model suite continues to improve overall. The main difference is with the 12Z UKMET being a little stronger with the surface low and more amplified with the 500mb trough axis. Slow moving closed low across the Southwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/EC mean/12Z NAM Confidence: Moderate A large and slow moving cut-off closed low in the southern stream situated near the southern California coast is expected to make little eastward progress through Friday evening, and likely making a small cyclonic loop, before gradually tracking eastward across the southern Rockies and eventually the western High Plains over the upcoming weekend. Both the 6Z and 12Z GFS runs are slightly faster in ejecting the closed low eastward across the southern Rockies and adjacent High Plains by Day 3. The 12Z UKMET retrogrades the upper low farther west during its cyclonic loop with little ensemble support. A blend of the 00Z ECMWF/00Z EC mean/12Z NAM best represents the model consensus. Upper level trough and cold front reaching the Northwest by end of the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z ECMWF Confidence: Moderate-High Shortwave energy along the southern coast of Alaska will progress eastward to the Yukon territory, and with the accelerating/exiting jet, the upstream ridge will break down and allow for greater propagation east and then southward across southwestern Canada. The height-falls will overspread the lee of the Canadian Rockies and then northern High Plains, and support a surface cold front to drop southward across Montana and the Dakotas. The main differences noted here are a more amplified 12Z NAM with the trough axis dropping south across the northern Rockies, and the 12Z UKMET is slightly faster with the progression of the cold front across the northern Plains. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick