Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Sun Apr 19 2020 Valid Apr 19/0000 UTC thru Apr 22/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Note...the 00z ECMWF was not available for this issuance. ...Track of the southern stream short wave... ...Surface low tracking across the Deep South to the Mid Atlantic Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 21/00z, 00z GFS/00z NAM/00z CMC thereafter Confidence: Average The 00z NAM/GFS are close to the consensus taking short wave energy from NM across the ArkLaTex to the Deep South through 20/00z. In fact, much of the 00z guidance is close with this feature and surface low development along the Mid Atlantic coast through 20/12z. The surface low tracks are about the same, so the main differences between the models remains the placement of the axis of highest rainfall, which has more to do with mesoscale interactions and the overlay of the instability and mid level lift. The 00z UKMET remains slower and left of the consensus with the surface low after 21/00z, likely due to the slower short wave energy in the developing trough. Because of this, this model was excluded from the preferred blend beyond that time. Because of the differences with the QPF placement and the track of the surface low off the coast, forecast confidence remains average. ...Short wave energy tracking across central Canada into the Upper Great Lakes... ...Developing long wave trough headed for New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 21/12z, 00z GFS/12z ECMWF after that Confidence: Slightly above average through 21/12z, slightly below average after that The 00z GFS/NAM are close to the consensus tracking short wave energy in the very fast mid level flow from Manitoba across the Upper Great Lakes through 21/12z. Beyond that time, the 00z NAM becomes slower with the developing long wave trough (which takes on a negative tilt) approaching northern New England. The 00z UKMET/CMC appear to have the same issue, while the 00z GFS/12z ECMWF are closer with the long wave trough and the surface low that starts deepening over Quebec toward the end of the period. Since the GFS/ECMWF have the support of their ensemble means, these solutions comprise the preferred blend. However, due to the spread concerning the evolution of the developing long wave trough, forecast confidence drops to slightly below average toward the end of the period. ...Developing long wave trough over the Southwest and Rockies Mon/Tue ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/00z UKMET/12z ECMWF blend Confidence: Slightly below average The 00z NAM/GFS are close to the model consensus dropping a positively tilted long wave trough from the Pacific Northwest across the Northern Rockies before 20/00z. In the wake of this short wave, mid level ridging develops from Central CA into the Pacific Northwest, peaking before 20/12Z before eroding ahead of the next short wave in the flow. The collapsing mid level ridge is resulting in some model instability concerning how quickly the next short wave crosses the CA coast before closing off in the mid levels over southern NV by 21/00z. The timing issues suggest that the 00z GFS may be too quick to open up the mid level closed low into a long wave trough crossing the Southern Rockies by 22/12z. In contrast, the 00z NAM/00z UKMET/12z ECMWF indicated a slower movement, which tracks better with a mid level closed low opening up and moving east. However, the details of how these models get to the final solutions may yet still change, considering how much spread there is in the evolution of the closed mid level system. Due to that spread, 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