Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1151 PM EST Mon Dec 02 2019 Valid Dec 03/0000 UTC thru Dec 06/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low impacting New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Differences with the deep layer cyclone still impacting New England are sufficiently minor that a general model blend can be preferred as the system pulls away on Tuesday. ...Upper low offshore the West Coast through Tuesday... ...Energy then crossing the southern tier through Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours 12Z ECMWF...after 36 hours Confidence: Slightly above average There is rather good agreement with the evolution of the upper low offshore the West Coast through about 36 hours, but thereafter the 00Z GFS becomes a relatively progressive outlier solution (common bias) as the energy traverses the southern tier of the nation going through Wednesday and Thursday. The GFS is also a bit deeper with surface low pressure that evolves across the southern Plains and lower MS Valley through the period. On the flip side, the 12Z CMC and 12Z UKMET overall are a little weaker than the model consensus by the end of the period, with the 12Z ECMWF splitting the difference between stronger and weaker camps. A general model blend should be fine with this system through 36 hours, but a preference toward the ECMWF is suggested thereafter with rather solid support also from the latest GEFS mean and ECENS mean. ...Next amplifying trough across the OH Valley/Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/GFS and 12Z ECMWF blend Confidence: Average The models amplify a shortwave trough down across the OH Valley and Northeast Tuesday and Wednesday. The 12Z UKMET and 12Z CMC are a tad deeper than the remaining model consensus, with the latest ensemble suite overall favoring the relatively weaker 00Z NAM/GFS and 12Z ECMWF. Although it should be noted that there are some GEFS members that do favor a deeper solution than this consensus. For now, will lean toward the relatively more modest camp. ...Weak shortwave/low clipping the Northern Plains Wednesday... ...Crossing the Great Lakes on Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Average The models support a weak shortwave and associated surface low/front clipping the northern Plains late Wednesday and quickly reaching the Great Lakes region by late Thursday. The 00Z NAM/GFS and 12Z UKMET solutions end up being more progressive with this system and relatively flatter compared to the 12Z ECMWF and especially the 12Z CMC. The ensemble means are a bit split with the timing, as the GEFS is more progressive and the ECENS cluster slower, but they all agree that the CMC is a deeper outlier. For now, a compromise leaning toward a non-CMC blend is suggested. ...Deep closed low offshore the West Coast by Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend...led by a 00Z GFS/12Z ECMWF blend Confidence: Above average The models support another very deep closed low evolving offshore of the West Coast by Friday. The 12Z CMC is displaced a bit northeast of the model consensus with its upper-level and surface reflections. The majority cluster of solutions suggest a system that will be a bit slower to advance east at the end of the period, which is strongly suggest by the GEFS and ECENS clusters. A non-CMC blend will be preferred with strong weighting toward a 00Z GFS/12Z ECMWF blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison