Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 151 PM EST Wed Feb 28 2018 Valid Feb 28/1200 UTC thru Mar 04/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...12Z model evaluation along with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave over the Southwest, ejecting eastward into the Plains tonight and reaching the East Coast late Thursday while interacting with a northern stream wave dropping south from the upper Mississippi valley... ...Resultant surface cyclone into the Ohio valley on Thursday with surface low reforming southeast of the New England coast through Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/GFS/ECMWF blend (even weighting) Confidence: Average 00Z GEFS/ECMWF/CMC ensemble spaghetti heights at 534 dam continue to show the GEFS and older runs of the GFS as stronger and on the western edge of the available members valid Friday across the Northeast. Ensemble trends in the heights and surface low plots have shown a western shift valid 12Z/02 offshore of New England with the GEFS members on the far northwestern edge and ECMWF members the southeastern edge of the envelope of solutions. The preference is to be near the centroid of the available ensemble scatter low plot positions, considering trends, which is between the 00Z GEFS and 00Z EC members, or near the 12Z NAM position valid 12Z/02. The 12Z models have continued to come into better agreement with the 12Z GFS and 12Z ECMWF converging toward one another, and lying a bit east of the 12Z NAM. Valid 00Z/03, the 12Z NAM ends up on the western side of the ensemble spread, and despite trends in that direction from the ensembles, blending with the farther east 12Z GFS and 12Z ECMWF appears prudent with the 12Z UKMET and 12Z CMC also depicting a farther east solution than the 12Z NAM. The 12Z UKMET appear a bit stronger or displaced away from idea concerning the ensemble spread. While some 12Z deterministic guidance has shown an eastward shift valid 12Z/02, trends had been west so we prefer to stay grounded toward a middle road approach. Regarding mass fields, the 12Z NAM/GFS/ECMWF look reasonably similar despite temperatures in the lowest kilometer or so above ground level, with the 12Z NAM coldest, 12Z GFS warmest and 12Z ECMWF in the middle. ...Large closed low off of the Pacific Northwest by Thursday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Similar to yesterday, there continues to be good agreement with this system. There have been some models that have trended a bit slower compared to yesterday's runs, but ensembles continue to show relatively good agreement, led by the consistent ECMWF mean. The 12Z UKMET backed off of a stronger surface low from its 00Z cycle which was considered unlikely in the preliminary preferences, so a general 12Z model blend is recommended for this system with slightly above average confidence given small spread and little run to run changes. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto