Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 150 AM EST Mon Dec 16 2019 Valid Dec 16/0000 UTC thru Dec 19/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level trough tracking from the central High Plains to the eastern U.S. through Wednesday morning... ...Surface low organizing east of the Mississippi River into Tuesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average ...07Z update... The 00Z ECMWF/UKMET/CMC trended toward one another while while the surface low offshore of New England continues to show some differences, a blend of the 00Z NAM/GFS/ECMWF/UKMET/CMC will provide a reasonable compromise. ...previous discussion follows... Minor timing differences remain with the 500 mb trough axis moving eastward along with latitude differences with the related surface warm front extending to the East Coast. The 12Z ECMWF/UKMET are slower while the 00Z NAM/GFS are faster. The 12Z CMC is also faster but displaced slightly farther south with the main axis of vorticity within the mid-level trough axis. At this point, a blend of the 00Z NAM, 00Z GFS and 12Z ECMWF match nearest to the middle of the latest model spread, but with slightly less weight on the 12Z ECMWF. As the surface low tracks offshore, the 00Z GFS appears too far north but the 12Z ECMWF too far south. Moderate spread remains in the ensemble scatter low plots which is preventing higher confidence with this system. ...Mid-level shortwave clipping the Great Lakes Tuesday Night and reaching New England late Wednesday...-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average ...07Z update... The 00Z UKMET adjusted to the remaining model consensus and little in the way of differences remain. Therefore, a general model blend is preferred. ...previous discussion follows... A deep but compact closed low swings through the northern Great Lakes region Tuesday. Model agreement is fairly good, but the 12Z UKMET stands out as a slow deterministic outlier. Better support exists for a non 12Z UKMET blend at this time. ...Trough approaching the western U.S. Tuesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/12Z ECMWF blend Confidence: Slightly below average ...07Z update... The 00Z UKMET and 00Z ECMWF sped up while the 00Z CMC slowed down with the 500 mb trough that reaches the West Coast. The 00Z ECMWF/UKMET consensus is just a bit faster than preferred given the latest ensemble spread. A blend of the 12Z/15 ECMWF and 00Z/16 ECMWF appears best for the western U.S. at this time. ...previous discussion follows... The latest models agree with a closed low within the base of a trough axis nearing the West Coast Tuesday night. Timing differences show up on Tuesday with the 00Z NAM slower and 12Z UKMET, 00Z GFS and 12Z CMC faster. Through Thursday morning, the 12Z CMC is fastest with the 00Z GFS next fastest. The 00Z NAM speeds up toward the middle while the 12Z UKMET slows down toward the middle by Wednesday evening. All in all, a middle of the road to slightly slower approach is favored given large ensemble spread and a trend to be slower. This placement is close to a 12Z ECMWF/UKMET blend from Monday through Thursday morning across the West. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto