Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1211 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 NAM/GFS evaluation along with preliminary 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: 12Z GFS / 00Z ECMWF blend through 00Z/02 00Z UKMET/ECMWF mean/06Z GEFS mean 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. The 00Z ECMWF is toward the slower side with the 00Z ECMWF mean a bit ahead of the deterministic ECMWF. The 12Z NAM is noticeably faster while the 00Z UKMET/CMC and 12Z GFS are near the middle through about 00Z/01. Beyond 00Z/01 (Wednesday evening), the 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 GFS looks reasonable until late in the day on Thursday when it trends toward the stronger side of the model spread considering GEFS scatter low plot strengths. 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 models are outliers. The 00Z ECMWF looks slower than ideal with the passage of the northern stream wave which impacts phasing and strength of the storm system downstream near New England. Unfortunately, no single deterministic model appears ideal here as they all seem to have issues in the way they evolve, but the 00Z UKMET may be the best of the deterministic guidance, especially by Friday morning near the Northeast with the ensemble trends in the scatter low plots leaving lots of room for changes. The 00Z UKMET blended with the 06Z GEFS mean and 00Z ECMWF mean seems best at this time, with the GEFS stronger and ECMWF weaker. ...Large closed low off of the Pacific Northwest by Thursday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models all show similarly here, 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