Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 138 AM EST Sat Dec 14 2019 Valid Dec 14/0000 UTC thru Dec 17/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deepening surface low over the Northeast today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Only minor timing and strength differences were seen with this system, therefore a general model blend is preferred. No significant changes were noted with the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...Mid-level trough amplifying into the western U.S. this weekend and reaching the central Plains Monday... ...Surface low organizing east of the Mississippi River Monday into Tuesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/ECMWF/UKMET blend Confidence: Slightly below average Timing differences at 500 mb show up in the deterministic guidance by Monday afternoon with the 00Z NAM outracing the remaining guidance across the Rockies. Looking at the ensemble spaghetti plots at 500 mb, the NAM does not show up as an outlier but does lie toward the faster end of the latest ensemble guidance (initialized 12Z/13). The 00Z ECMWF and 00Z UKMET trended slightly faster and a bit north with the downstream warm front on Monday relative to their previous 12Z cycles. Trends in the ensembles over their past 4 12/00Z cycles show opposing trends with the GEFS faster and ECENS slower. Therefore, the preference is to be in the middle of the latest ensemble spread, which is near a blend of the slightly faster 00Z GFS/00Z UKMET and somewhat slower 00Z ECMWF. Poor run to run consistency lowers confidence below average. ...Mid-level shortwave nearing the Upper Mississippi Valley Tuesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models are in decent agreement with this system through Tuesday morning. The 00Z CMC adjusted northward with the mid-level vorticity maximum in the vicinity of the Upper Mississippi Valley 12Z/17. The 00Z deterministic spread is small enough to allow for a general model blend with this system. However, ensemble spread is somewhat greater than the relatively good 00Z model agreement would suggest so confidence is only average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto