Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 114 PM EDT Sun May 31 2020 Valid May 31/1200 UTC thru Jun 04/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper level trough and cold front across the Eastern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Tuesday Confidence: Average While difference continue to develop downstream across Atlantic Canada, models remain in good agreement with the evolution of the upper trough as it continues to swing across the Northeast U.S. through early Tuesday. Upper level low slowly lifting from northern Mexico into the southern Plains Sunday-Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Overall, models are in generally good agreement - showing a broad upper low drifting north across the southern Plains through early Tuesday before weakening as remnant energy spreads east into the lower Mississippi valley on Wednesday. Shortwave lifting across the Pacific Northwest into central Canada late Sunday into early Monday, then dropping southeast into the Northeast U.S. late Tuesday into early Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend, but with less weight given to the 12Z GFS or 00Z ECMWF late Tuesday and Wednesday Confidence: Below Average Models are in good agreement through early Monday, showing the shortwave trough currently over the Pacific Northwest lifting northeast across the Canadian Rockies and into central Canada by early Monday. Timing and amplitude differences begin to develop as the system begins to weaken and move east across the top of an upper ridge, before spilling southeast across northern Ontario and western Quebec into the Northeast U.S. Tuesday night into Wednesday. Difficult to completely rule out any solution; however, suspect the 00Z ECMWF is probably too amplified given the confluent flow. This is further supported by the less amplified 00Z EC Ensemble Mean. Also, the 12Z GFS looks be a little slow, both with the weak wave dropping southeast into Northeast U.S. Wednesday morning and with the trailing front extending back across the Great Lakes. Again, the progressive nature of the flow, along with the model consensus would tend to support something faster. Upper level trough moving from the Pacific Northwest Monday to the northern Plains and Upper Midwest Tuesday-Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Lean toward the 00Z UKMET/ECMWF/EC Ensemble Mean Confidence: Below average Models continue to show timing and amplitude differences with this feature, especially as it moves east of the Cascades Monday night. By late Monday as the system moves across the Pacific Northwest, the NCEP guidance is generally deeper than the overnight runs of the UKMET, ECMWF and EC Ensmean. This continues downstream across the northern Rockies and through the northern Plains and upper Midwest, with the NCEP guidance becoming slower as well than the flatter UKMET, ECMWF and EC Ensmean. Given the progressive nature of the flow, recommend leaning toward the faster/flatter solutions. Cut-off low developing west of Southern California early in the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Lean toward the 00Z ECMWF/EC Ensemble Mean Confidence: Slightly above average Models are in good agreement indicating a closed, cut-off low developing off of the Southern California and northern Baja California coasts late Monday into early Tuesday. There are still some model differences with respect to position later in the period, with most of the guidance indicating a center southwest of the 12Z GFS and 06Z GEFS Mean. Compared with its 00Z run, the GFS is showing some shift in that direction as well - lending support for a more southwesterly solution, such as the 00Z ECMWF and EC Ensemble Mean. Shortwave moving across western Canada and the northwestern U.S. late Tuesday-early Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Lean toward the 00Z ECMWF/EC Ensemble Mean Confidence: Slightly above average The NCEP guidance, especially the GFS, is more amplified than the general deterministic and ensemble consensus as the system moves east of the Rockies into the Canadian Prairie and U.S. High Plains Wednesday morning. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Pereira