Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1145 AM EST Tue Jan 30 2018 Valid Jan 30/1200 UTC thru Feb 03/0000 UTC ..See NOUS42 KWNO (ADMNFD) for upper air ingest status... 12Z NAM/GFS evaluation with preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Departing longwave trough and surface low from the eastern U.S. this evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average The models show similarly with this system. ...Cold front moving through the northern Plains today, Great Lakes on Wednesday, and lower Mississippi valley to the Mid-Atlantic Thursday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Slightly above average The differences with the cold front are somewhat subtle, and relate to the timing as the boundary crosses the Great Lakes region. Through Thursday night at least, the 12Z GFS appears a little fast, but these differences are minor and within an acceptable range. Therefore, a general model compromise appears reasonable for this system. ...Surface low development with impacts to the Northeast Thursday night into Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/CMC blend Confidence: Average Similar to the previous system, the differences here are somewhat subtle but ensemble scatter low plots show the 12Z GFS toward the south side of the available members and the 12Z GFS is also on the south side of the latest deterministic models as well. The 12Z NAM appears stronger and is on the northwestern edge of the latest ensemble surface lows by 12Z/02. The 00Z ECMWF is a little slower to develop the surface wave, while the 00Z CMC is a bit faster and south of the ECMWF. A blend of the 00Z ECMWF/CMC appears the best route given placement in the middle of the latest ensemble members and near the center of where trends in the ensemble data is pointing. ...Weakening mid-level shortwave approaching the Northwest on Friday along with preceding onshore flow... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS / 00Z ECMWF blend Confidence: Average Differences are small until late Friday with the timing of the shortwave trough. The ensemble means support a blend of the 12Z GFS and 00Z ECMWF while the 12Z NAM appears faster and 00Z UKMET/CMC are south of the means. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto