Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 144 PM EST Thu Feb 01 2018 Valid Feb 01/1200 UTC thru Feb 05/0000 UTC Valid Feb 1/1200 UTC through Feb 05/0000 UTC ..See NOUS42 KWNO (ADMNFD) for upper air ingest status... ...12Z model evaluation with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Cold front moving across the Great Lakes through the MS Valley tonight into Fri... ...Surface low pressure forming on the front over southwest Quebec into northern New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF blend Confidence: Average The 12Z NAM was close to the model consensus with a short wave tracking from the upper Great Lakes into northern New England tonight into Fri, but speeds up across northern New England during Fri/Fri night. Surface low pressure forming on the front ahead of the short wave deepens much more quickly across northern New England Fri into Fri night, which is a model bias for the NAM. The 12Z GFS was closer to the consensus with the short wave and surface low as they cross northern New England Fri night Fri night. Its solution is close to the 12z ECMWF, as well as the ensemble means of each of these solutions. Because of this, a blend of the 12Z GFS/12Z ECMWF was the preferred solution. ...Short wave crossing the Pacific Northwest Fri into Fri night, before tracking into the Rockies during Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF/12Z UKMET blend Confidence: Average The 12Z NAM is initially close to the consensus as the short wave crosses WA and northern Rockies during Fri into Fri night. After that time, the 12Z NAM becomes faster and deeper with the short wave as it crosses the central and southern Rockies. By contrast, the 12Z GFS solution is closer to the 12z ECWMF/UKMET throughout the life cycle of the short wave...which reaches the southern Plains by 00z Sun. These solutions are supported by the ensemble mean solutions as well. ...Short wave tracking from western Canada into the northern Plains, reaching the upper Great Lakes Sun... ...Surface low pressure forming on a frontal boundary over western New England Sun into Sun night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF blend Confidence: Slightly below average The 12Z NAM is close to the consensus as the short wave tracks out of western Canada into the northern Plains Fri into Sat, but it becomes faster and deeper with the short wave as it crosses the upper Great Lakes by 05/00z. Because of this, its developing surface low becomes deeper and faster as it crosses into southwest Quebec Sun evening. The 12Z GFS remains closer to the consensus through 12z Sun, then becomes slower than the consensus through 00z Mon with its mid level short wave and surface low (the slowing is supported by the 00z GEFS mean). The 12Z ECMWF is somewhere in the middle of the 12Z NAM/GFS solutions, and is supported by the 00z ECWMF mean. The WPC preference is for a 12Z GFS/12Z ECWMF blend, in an attempt to mitigate some of the timing differences. However, because of the model spread, forecast confidence remains below average. ...Short wave energy tracking from the southern Plains across the Southeast Sat into Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average There was good model consensus with the short wave tracking out of the southern Plains Sat into the Southeast during Sun, and there is similarity with respect to the placement of the axes of maximum QPF across the Southeast Sat night into Sun. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes