Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1249 AM EDT Tue May 05 2020 Valid May 05/0000 UTC thru May 08/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z NAM/GFS Model Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Series of mid-level shortwaves tracking across the Midwest through Tuesday night, consolidating over the Mid-Atlantic late Wednesday... ...Surface low development off of the East Coast Wednesday/Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend (least weight on 00Z GFS Wed - Thu morning) Confidence: Average A pair of vorticity maxima over the Midwest today will transition eith eastward extent into a strengthening mid-level trough by Wednesday morning. The 00Z GFS is strongest with the 850-500 mb low and also farther north than the consensus. This is noted roughly from Wednesday to Thursday morning. As the trough axis moves offshore, surface low pressure will organize and track north-northeastward, offshore of the Northeast coast. There remains some north-south and east-west spread in the latest ensemble scatter lot plots with the 12Z UKMET/CMC on the western side of the ensemble lows. The 18Z GEFS mean is also on the western side. Therefore, a general model blend should pull weight toward the middle of the latest model spread, east of the 12Z UKMET/CMC but west of the 12Z ECMWF. ...Mid-level shortwave moving from Pacific Northwest Coast Tuesday night across the northern Rockies Wednesday night and the northern Plains Thursday... ...Cold front dropping southward through the Great Plains on Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, 12Z UKMET blend Confidence: Slightly Above Average There is more separation with mid-level vorticity maxima embedded within a shortwave trough along the West Coast Wednesday morning in the 00Z NAM than the remaining model guidance. The 00Z NAM ends up faster with this lead vorticity max/shortwave as it traverses the western ridge and amplifies into the Central Plains. The non-00Z NAM guidance shows decent agreement but the 12Z CMC differs in the way its shortwave evolves, holding more energy back toward the west while the consensus is for more strength toward the east valid Thursday morning at 500 mb. The 00Z GFS is by far the strongest, depicting a robust mid-level shortwave as it nears the Mississippi Valley Friday morning. The GFS's resultant surface low is likely too strong and lies on the southern side of the ensemble spread. However, the similarly timed 12Z UKMET looks too weak/sheared with the feature and lacks a defined surface low. The 12Z ECMWF is in the middle of the strength depicted by the 00Z GFS and 12Z UKMET. A 3-way blend of the 00Z GFS, 12Z ECMWF and 12Z UKMET looks reasonable but minding the differences in strength of the shortwave...which extend from the surface to the tropopause. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto