Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 237 PM EST Tue Feb 27 2018 Valid Feb 27/1200 UTC thru Mar 03/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...12Z model evaluation along with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern Stream shortwave crossing the northern Plains through Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Through much of Wednesday night, the models have converged to a common solution compared to yesterday, with the non-NCEP guidance moving toward the NAM/GFS. Beyond about 12Z Thursday, there are differences with the interaction of this wave and a southern stream feature; discussed below. ...Closed low over the California coast today...becoming an open wave as it tracks into the southern Plains late Wednesday... ...Resultant surface cyclone into the Ohio valley on Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-12Z NAM blend through 00Z/02 12Z ECMWF/UKMET/CMC blend 00Z/02-03 Confidence: Below average While some minor spread remains in the ensemble spaghetti plots, there has been decent run to run consistency from the past 3 cycles regarding the southern stream shortwave as it reaches the southern Plains Wednesday night. The 12Z ECMWF sped up slightly compared to the slower 00Z ECMWF...with the 00Z ECMWF and 12Z UKMET toward the slower side of the models and the 00Z ECMWF mean a bit ahead of both the 00Z and 12Z deterministic ECMWF. The 12Z NAM was noticeably faster while the 12Z GFS was near the middle through about 00Z/01. Beyond 00Z/01 (Wednesday evening), the 00Z ECMWF/UKMET/CMC have trended away from a more amplified northern stream wave which 12Z NAM shows as rather deep over the Ohio valley Thursday night as it phases/interacts with energy streaking across the middle Mississippi valley. The 12Z ECMWF?UKMET/CMC stayed the course which makes the 12Z NAM seem unlikely in the way it evolves across the upper Midwest/Ohio Valley. The 12Z GFS looks reasonable until late in the day on Thursday when it trends toward the stronger side of the model spread considering ensemble spaghetti ensemble plots. The GFS appears too strong/north with its low placement in New England by 12Z/02 as it is on the stronger side of the ensemble guidance but none of the deterministic models are outliers. Unfortunately, no single deterministic model appears ideal here as they all seem to have issues in the way they evolve. However, the 12Z ECMWF/UKMET/CMC trended in the direction of the 12Z NAM/GFS but not to their extremes. While differences remain among the 12Z ECMWF/UKMET/CMC...a blend of these three models appears best at this time, especially by Friday morning near the Northeast with the ensemble trends in the scatter low plots leaving lots of room for changes. ...Large closed low off of the Pacific Northwest by Thursday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Despite some timing/strength differences, the models all show similarly with the large closed low along the West Coast, enough for a general model blend with decent ensemble agreement. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto