Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1130 PM EST Sun Feb 16 2020 Valid Feb 17/0000 UTC thru Feb 20/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Initial Model evaluation with preferences & confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper trough crossing the Northeast on 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 Northeast on Monday, with an attendant cold front crossing New England by Monday night. There is enough mass field agreement in the models to merit a general model blend for this feature. Shortwave impulse and surface low across Upper Midwest Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF 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. The main difference in the models is with the 12Z CMC, indicating a flatter trough and a suppressed surface low across the Great Lakes region. The 12Z UKMET is slightly slower with the progression of the cold front and farther north with the low over the Great Lakes region. There is enough agreement among the GFS and ECMWF to merit a blend of those two models as a starting point in the forecast. Second shortwave impulse reaching the Great Lakes Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/GFS/18Z GEFS mean 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 12Z UKMET is slower and the CMC is weaker. There is very good agreement among the 00Z NAM, GFS, and 18Z GEFS mean to warrant a blend of these models to start with. Broad upper level trough building across the Intermountain West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF/12Z EC mean Confidence: Slightly below 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. Most of the model differences become apparent after 60 hours, with the UKMET indicating the greatest degree of undercutting, and the NAM is stronger across the northern Rockies and Great Basin by Day 3. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick