Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 AM EDT Fri Apr 17 2020 Valid Apr 17/0000 UTC thru Apr 20/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Short wave energy tracking from the Rockies to Southern New England... ...Surface low pressure crossing the Ohio Valley into northern Mid Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 00z NAM/GFS are close to the model consensus with short wave energy tracking out of the Rockies across the OH Valley before taking it off the southern New England coast. They are also similar spinning up surface low pressure on a front here, which tracks south of southern New England after 18/12z. After that time, the 12z ECMWF remains west off the consensus surface low track, and becomes slower with time. However, much of the sensible weather with the surface low at this time is offshore, so a general model blend is preferred with slightly above average confidence. ...Short wave energy in the southern stream... ...Surface low tracking from the Southern Plains to the Mid Atlantic coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-12z GEFS blend Confidence: Average The 00z NAM/GFS are close to the consensus as they take a weakening mid level trough across Southern CA and the Southwest through Sat before weakening it. A second short wave following in the wake of the first moves across Southwest into the Southern Plains. Initially, the 12z ECMWF/UKMET are slower with the second short wave (as they have been for the past three model cycles), but get closer to the 00z NCEP guidance across the Deep South after 19/12z. The short wave aids in spinning up surface low pressure over the Southern Plains at 19/12z. Though there are some model differences (which are mainly latitudinal in nature) with the track of the surface low, there is better model consensus deepening the low after it reaches the western edge of the Gulf Stream toward 20/12z. The differences in the track are within the noise at this distance, but could have significant impacts in the placement of the highest rainfall axis during Sun/Sun night. Based on the above, a multi model blend is preferred, minus the 12z GEFS, which curiously trails the multi model placement of the surface low after 20/00z. Given that there are some track details remaining (which could have impacts on the QPF), forecast confidence is average. ...Short wave energy in the northern stream from Manitoba into the Upper Great Lakes... ...Attendant cold front crossing the Northern Plains into the Upper Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-00z NAM blend Confidence: Slightly above average Both the 00z NAM/GFS are close to the consensus with short wave energy tracking from central Manitoba into the Upper Great Lakes after 19/00z. Despite the general agreement in the mid level timing, the 00z NAM continues that model's trend for a slower cold frontal passage across the Northern Plains into the Upper Great Lakes through 20/12z. Based on the good model clustering otherwise, a non-00z NAM blend is preferred with slightly above average confidence. Short wave over the Pacific Northwest Sat into Sun ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z ECMWF blend Confidence: Slightly below average Short wave energy dropping south across western British Columbia after 19/12z begins to break down mid level ridging in place over the Pacific Northwest Sat into Sun. The 00z NAM/GFS are close to the consensus with this feature, though the 00z NAM weakens the feature, as it is weaker with the mid level ridge building just west of it. As the system briefly closes off over WA/OR, the next short wave in the flow sends the mid level system southeast across the Northern Rockies. There is a fair amount of spread how this occurs, as short wave energy undercuts the mid level ridge over the Pacific. The 00z GFS/12z ECMWF offer a loose consensus with this feature, but given the spread concerning how the mid level system evolves after 19/12z. forecast confidence is slightly below average, Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes