Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1241 AM EDT Wed Apr 03 2019 Valid Apr 03/0000 UTC thru Apr 06/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Powerful surface low lifting up off New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in reasonably good agreement with the details of the powerful surface low offshore of the Mid-Atlantic states which will quickly lift northeast up offshore New England early Wednesday and then exit into southeast Canada. The 00Z GFS/NAM solutions do become a tad more progressive than the 12Z UKMET/CMC/ECMWF solutions as the low center moves across Nova Scotia, but a general model blend should suffice to resolve these modest timing differences. ...Shortwave reaching the Four Corners on Wed... ...Cyclogenesis over the Southern Plains by Thurs... ...Energy shearing toward the OH/TN Valleys by Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/GFS and 12Z ECMWF Confidence: Average The models handle this feature similarly through early Thursday with at least some modest timing and depth differences by late Thursday as the 12Z ECMWF begins to slow its shortwave evolution down just a bit, and the 00Z NAM begins to become a tad stronger than the remaining guidance. The 00Z GFS begins to outrun the model consensus by just a tad by Friday as the energy reaches the OH/TN Valleys. At the surface, the guidance shows good agreement with the low center over the southern Plains, but as the system dampens out toward the OH/TN Valleys, there is some spread with the details of weak low pressure. The 00Z NAM/GFS and 12Z ECMWF all tend to hang onto somewhat of a more defined low that at least lifts up across OH Valley and toward the lower Great Lakes region and this is supported by the latest GEFS mean and ECENS mean. The 12Z CMC/UKMET solutions are more diffuse/weaker. Accommodating some of the timing/depth spread, a blend of the NAM/GFS and ECMWF will be preferred. ...Shortwave troughs approaching the West Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...led by 00Z GFS/12Z ECMWF Confidence: Average Models show agreement that a shortwave should reach the West Coast by late Thursday, with another following in rapid succession on Fri. Solutions differ a bit on the separation between these features and on the structure (closed upper low or negatively tilted but more progressive trough). What seems clearer is that as the leading wave encounters broad anticyclonic upper-level flow across the Great Basin/Rockies, energy should separate out with a southern stream component crossing reaching the Four Corners region by Friday. The 12Z ECMWF/UKMET solutions become a bit slower than the 00Z NAM/GFS and 12Z CMC with the southern stream extension by Friday. The northern stream based energy coming across the Pacific Northwest tends to be a bit better agreed upon among the models. Will recommend a general model blend at this time, led by a blend of the 00Z GFS and 12Z ECMWF which will be also be supported by the latest GEFS mean and ECENS mean. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison