Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1149 AM EST Sun Dec 15 2019 Valid Dec 15/1200 UTC thru Dec 19/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level trough tracking from the western U.S. to the eastern U.S. Wednesday morning... ...Surface low organizing east of the Mississippi River Monday into Tuesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/ECMWF blend Confidence: Average Fairly good agreement now exists between the global models with the storm system moving through the central/eastern U.S. over the forecast period. Aloft, there is little difference between the various models for the strength and position at 500/300 mb. Some differences remain at the surface, particularly as the low moves offshore the Northeast / New England coasts. The CMC is slower and further south while the GFS is a touch faster. But overall a general model blend should yield a reasonable solution. ...Mid-level shortwave clipping the Great Lakes Tuesday into Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average A deep but compact closed low swings through the northern Great Lakes region Tuesday. Model agreement is above average now. Some minor differences develop with the surface low track (GFS a bit south compared to the consensus) but overall a general model blend will suffice for this area during this time. ...Trough approaching the western U.S. Tuesday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/ECMWF blend Confidence: Below average There continues to be fairly sizable differences in the model guidance with the next system to move through the western U.S. Tuesday night into Wednesday. Ridging aloft initially is of similar strength/position by the global models, but a mid/upper level shortwave will near the coast Tuesday. Some guidance advertises this as a closed low while others remain open. The 00Z UKMET and 00Z CMC were the fast outliers and mostly removed from the blend preference. At the surface, wavy low pressure will lift well north of the 500 mb shortwave and there are some considerable differences here. As such, will lean on a GFS/ECMWF blend primarily, with some inclusion of the CMC through 60 hours. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor