Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 336 AM EDT Thu Apr 30 2020 Valid Apr 30/0000 UTC thru May 03/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low impacting the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/CMC blend Confidence: Average The 00Z NAM digs the center of the closed low impacting the eastern U.S. farther south than any other guidance which results in a slower and southward displaced 500 mb trough in the NAM by early Saturday. The 00Z NAM is a total outlier with the mid-level trough axis by 12Z Saturday compared to all of the ECMWF/GEFS/CMC ensemble members. The 00Z GFS is faster with a lead vorticity max located on the eastern edge of the mid-level trough axis Friday morning which when combined with a faster shortwave trough axis approaching northern New England Friday night causes the lower levels of the 00Z GFS to fall out of alignment with the remaining model consensus and middle ground 12Z ECMWF ensemble mean. The 00Z ECMWF/UKMET/CMC are in good agreement with this system and match closer to the middle of the latest ensemble spread with the upper trough evolution. ...Shortwave crossing the Northwest today and moving into western Ontario Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/CMC blend Confidence: Slightly above average The 00Z GFS stands out the greatest with a more amplified and slower 500 mb shortwave track by mid-day Friday. The 12Z UKMET is somewhat similar to the GFS, but the 00Z UKMET jumped north with the track of the vorticity max. However, trends from the 00Z ECMWF and 00Z CMC were in the direction of the 00Z GFS (just not as extreme) and so the 00Z NAM appears to be less favorable at this time. A 00Z ECMWF/UKMET/CMC blend will incorporate some of these new trends which fall between the northern and faster 00Z NAM and southern/slower 00Z GFS. ...700-500 mb shortwave reaching the central Plains Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/CMC blend Confidence: Below average No significant changes were noted with the 00Z ECMWF/UKMET/CMC regarding this feature. A subtle low to mid-level shortwave is expected to reach the central Plains early Saturday with an axis of 700 mb convergence into the Great Plains. The 00Z NAM/GFS are south with this feature compared to the 00Z ECMWF/UKMET/CMC. 500 mb heights from the latest ensemble spaghetti plots support the northern non-NCEP camp more so than the NAM/GFS. This feature will be occurring in a post-frontal environment with upslope flow just above the surface. Convective uncertainty lowers confidence with this feature but a Southern Plains surface low now shows good model agreement from the latest available models. ...Deep trough offshore the West Coast by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z UKMET blend Confidence: Average Ensemble means support a non 00Z UKMET blend with the approaching large trough/closed low offshore of the Pacific Northwest early Saturday. The 00Z UKMET is faster than the remaining consensus and the 00Z CMC adjusted the base of the trough (compared to its 12Z run) to fit into the non 00Z UKMET consensus. Despite the decent agreement from the 00Z models, ensemble spaghetti plots still show some spread and room for future adjustments with later deterministic guidance. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto