Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 149 AM EST Sun Feb 16 2020 Valid Feb 16/0000 UTC thru Feb 19/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model evaluation with preferences & confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper trough across Great Lakes and Northeast Sunday and Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Broad cyclonic flow aloft over the north-central U.S. will support the passage of a few shortwave perturbations through the beginning of the work week. The lead impulse will track eastward across the Great Lakes on Sunday and then the Northeast on Monday, with an attendant cold front reaching northern New England by Monday morning. There is enough mass field agreement in the models to merit a general model blend for this feature. Shortwave impulse across Upper Midwest Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/GFS blend Confidence: Slightly above average By Monday evening the upper level flow pattern is expected to become more separated with a northern and southern stream component. Two separate shortwaves in quick succession are progged to cross the Upper Midwest and northern Great Lakes region, with the first one tracking eastward across the Upper Midwest and the Dakotas on Monday, and then reaching the northern Great Lakes by early Tuesday. This will support a wave of low pressure along a cold front across this region. Similar to yesterday, the 00Z NAM remains stronger and slower with the passage of the trough axis, and its surface low is north of the model consensus across the Great Lakes. The 00Z UKMET is slower with the progression of the cold front across the Ohio Valley and the Appalachians. The GFS and ECMWF are close to their respective ensemble means, and a blend of these two models should suffice as a starting point. Second shortwave impulse reaching the Great Lakes Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/CMC Confidence: Near average A mid level impulse will quickly follow in progressive northwest flow over northern Minnesota and northern Michigan on Tuesday, and eventually consolidate with the previous shortwave mentioned above. The main difference in the models is the 00Z NAM is slower and stronger with the trough passage, and the GFS is slightly faster. The 00Z ECMWF and CMC remain the best starting point for mass fields. Broad upper level trough building across the Intermountain West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET/00Z GFS/00Z CMC Confidence: Near average The southern stream component of the upper level flow is forecast to evolve into a broad trough over the Intermountain West by Monday night whilst an upper level ridge axis builds just west of the West Coast. Some of the shortwave energy may try to undercut the ridge and form a temporary blocking pattern. The 00Z NAM is also more amplified with this portion of the trough, whilst the EC mean does not show as much tendency to undercut the West Coast ridge by Wednesday morning. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick