Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 234 PM EDT Wed Apr 03 2019 Valid Apr 03/1200 UTC thru Apr 07/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Powerful surface low pulling away from New England today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Model solutions handle this feature similarly as it races toward the Canadian Maritimes by this evening. A general model blend should resolve any very minor differences among solutions. ...Shortwave crossing the Four Corners today... ...Cyclogenesis over the Southern Plains by Thu... ...Shortwave/surface low crossing the Ohio Valley Fri... ...Potential surface low developing along the Southeast coast Fri night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/ECMWF blend Confidence: Average The trend over the past 24 hours has been toward a somewhat weaker shortwave emerging from the Rockies to the Central Plains early Thu, with the GFS/NAM solutions coming around to something more like the ECMWF/CMC/UKMET showed yesterday. Model solutions now handle the shortwave similarly through Thu night, before the NAM becomes slightly quicker than consensus with moving the wave eastward. With respect to the weak surface low expected to develop across the Southern Plains on Thu and then move northeastward, a blend of the GFS and ECMWF should provide a solution that is close to the consensus of ensemble members. A number of ECENS and CMCE members hint at the potential energy to transfer to a relatively weak coastal low along the Southeast or southern Mid-Atlantic coast by late Fri/Fri night, while this feature is noticeably absent in the GFS or any GEFS members. Given the presence of this features in 2/3 ensemble systems, it seems like at least a distinct possibility, and a blend of the GFS and ECMWF should hint at the potential for such a feature. ...Active Pacific upper-level jet reaching the West Coast with series of embedded shortwaves... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Sat ECMWF/UKMET/CMC blend after 00Z Sat Confidence: Average through 00Z Sat, below average after 00Z Sat An increasingly active flow regime is expected to evolve along the West Coast over the next few days, with a series of upper-level shortwaves arriving as a strong North Pacific jet approaches the region. Models show relatively good agreement as the first couple waves arrive Thu night-Fri, and a southern stream component shears east across the Southern Tier. As the third shortwave, associated with the strongest upper jet, approaches the Pacific Northwest on Sat, model solutions diverge on the amplitude and timing of the feature. The past couple ensemble cycles show a modest trend toward a more amplified wave arriving Fri, as shown by the ECMWF/UKMET/CMC, although all models have shown some degree or run-to-run variability here. At this time, will recommend a general model blend prior to 00Z Sat, and given the trend, will go with a more amplified wave reaching the Northwest on Fri as shown by the ECMWF/UKMET/CMC. ...Southern stream shortwave crossing the Southwest Fri and reaching the central U.S. Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Sat ECMWF/UKMET blend after 00Z Sat Confidence: Average through 00Z Sat, below average after 00Z Sat Models show modest timing/amplitude differences as this feature crosses the Southwest U.S. on Fri, with differences increasing by Sat as the wave moves into the Southern/Central Plains. Given run-to-run variability and no clear trends evident in the ensembles, will prefer solutions generally close to an ensemble mean-based consensus at this time. Means support a somewhat slower progression than the GFS/NAM, more along the lines of the ECMWF/UKMET. A surface low seems likely to take shape somewhere across the central U.S. on Sat as the upper wave approaches, but given differing evolutions aloft confidence is low as to exactly where any potential surface low might develop. This spread is beared out in the ensemble low scatter plots, which show member lows everywhere from West Texas to the Midwest at 00Z Sun. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Ryan