Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 311 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 Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low impacting the East through Friday and early Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~ Preference: 30/12Z ECMWF/EC Ensemble Mean/CMC blend Confidence: Average The models were in decent agreement with the progression of the trough through about 00Z Saturday...at which time the NCEP guidance becomes faster than non-NCEP guidance. By that point, a majority of the differences in placement and strength are out at sea...although those differences also have impacts upstream of New England. The 30/12Z ECMWF and UKMET both accelerated the trough axis compared with their previous runs but they remained slower than the NCEP guidance. At this point, the latest ensembles still support the non-NCEP operational solutions...so our preference remains with the ECMWF/Ensemble mean and Canadian. ...Shortwave crossing the Northwest today and moving into western Ontario Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 30/12Z 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...at odds with trends from the 30/12Z ECMWF and 30/00Z CMC. The lower mid-level heights in the GFS also made it easy for a second shortwave originating in northern Saskatchewan to drop southeastward and produce a deepening closed mid-level low over Ontario and Quebec by early Sunday. While the mid-level height pattern in the ECMWF and UKMET leaves room for a spot-low, neither of them develops a deepening mid- and upper-level low like the GFS. As a result, will continue to favor a blend of the 30/12Z ECMWF/UKMET/CMC. ...700-500 mb shortwave reaching the central Plains Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 30/12Z ECMWF/UKMET/CMC blend Confidence: Average The 12Z suite of NCEP and non-NCEP guidance alike maintained decent continuity with their respective runs...meaning that the NAM and GFS were south with this feature compared with the non-NCEP guidance. The latest ensemble spaghetti plots still offer more support to the non-NCEP guidance...so no changes to the model preference was made. Convective uncertainty lowers confidence with this feature. ...Deep trough offshore the West Coast by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 30/12Z UKMET blend Confidence: Average Despite the decent agreement from the 30/12Z models...ensemble spaghetti plots still suggest that a non-UKMET blend will work best. Enough spread remained to allow for adjustments in the future. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Bann