Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1148 PM EST Fri Dec 13 2019 Valid Dec 14/0000 UTC thru Dec 17/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation with Preliminary 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. ...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, 12Z ECMWF, 12Z 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). 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/12Z UKMET and slower 12Z ECMWF. Poor run to run consistency lowers confidence below average. ...Mid-level shortwave nearing the Upper Mississippi Valley Tuesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z CMC blend Confidence: Average The models are in decent agreement with this system outside of the faster 12Z CMC. However, ensemble spread is somewhat greater than the non 12Z CMC agreement would suggest. Therefore, a non 12Z CMC blend is preferred given stronger support for a solution slower than the faster 12Z CMC, but with only average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto