Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1253 PM EDT Thu Apr 30 2020 Valid Apr 30/1200 UTC thru May 04/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low impacting the East through Friday and early Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~ Preference: 00Z ECMWF/EC Ensemble Mean/CMC blend Confidence: Average The 12Z GFS continued to be on the faster side of the guidance in bringing a shortwave on the eastern edge of the mid-level trough ejecting of the eastern U.S. as well as being faster to bring a second vorticity center towards New England on Friday. The NAM was also inclined to stick with its southward-displaced trough like it showed in its 30/00Z run. Both features were outliers with the mid-level trough axis by 12Z Saturday compared to all of the ECMWF/GEFS/CMC ensemble members. Removed the 30/00Z UKMET from the choice given its very slow progression. ...Shortwave crossing the Northwest today and moving into western Ontario Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 30/00Z ECMWF/UKMET/CMC blend Confidence: Slightly above average The GFS from the 30/12Z run still stands out the greatest with a more amplified and slower 500 mb shortwave track by mid-day Friday...which still puts it at odds with trends from the 30/00Z ECMWF and 30/00Z CMC (those non-NCEP models were showing some trends toward that general solution but there were just not as extreme). The lower mid-level heights in the GFS also made it easy for a second shortwave originiating in northern Saskatchewan to drop southeastward and produce a deepening closed mid-level low over Ontario and Quebec by early Sunday. At this point, thinking is that a 30/00Z ECMWF/UKMET/CMC blend will incorporate some of these ideas which fall between the northern and faster 30/12Z NAM and southern 30/12Z GFS. ...700-500 mb shortwave reaching the central Plains Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 30/00Z ECMWF/UKMET/CMC blend Confidence: Below average The 30/12Z NCEP runs were similar to their previous runs...meaning that they were south with this feature compared with the 30/00Z runs of non-NCEP guidance. The latest ensemble spaghetti plots still offer more support to the non-NCEP guidance at this point. No change to the overall preference was made. 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 30/00Z 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. Despite the decent agreement from the 30/00Z models and the 30/12Z run of NCEP 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 Bann