Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 111 PM EDT Wed Apr 22 2020 Valid Apr 22/1200 UTC thru Apr 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream trough exiting the Southern Plains and crossing the OH Valley Thursday and Mid-Atlantic Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET/ECMWF and 00Z ECENS with some 06Z GEFS and 00Z CMC blend Confidence: Average The southern stream mid-level trough over the southern Plains today reaches the middle MS Valley tonight. This energy along with a deepening surface low center will then advance northeast and cross the OH Valley Thursday and push off the northern Mid-Atlantic coast Friday as an attendant cold front sweeps across the South. The 12Z GFS has dramatically slowed this system from being one of the fastest to the slowest and remains farther north with its surface low track over the OH Valley/Mid-Atlantic and is thus not preferred. The 12Z NAM remains the fastest solution with the trough and surface low and is thus also not preferred. The 00Z CMC is the weakest with its surface low, but is in line with the 00Z ECMWF and UKMET for low track. Regarding timing and depth of the system, the 00Z UKMET and 00Z ECMWF have better ensemble support (06Z GEFS/12Z ECENS means). So, will favor a blend of the UKMET/ECMWF solutions and along with a preference for the 00Z ECENS ensemble mean along with some inclusion of the 06Z GEFS and 00Z CMC for the time being. ...Northern Stream Shortwave/Low center across the Northern Plains tonight/Thursday and Midwest Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/CMC Confidence: Average Guidance brings a northern stream shortwave and associated low center down from Canada and across the eastern Dakotas tonight into Thursday and then attempt to amplify it a bit over the Midwest on Friday. The 00Z UKMET is the strongest solutions with this energy. While most of the models generally dissipate the low center, the UKMET actually holds on to a rather well-defined low center over the Midwest going into Saturday. The 12Z NAM/GFS and 00Z CMC/ECMWF are all weaker and generally favor the southern stream low over the TN Valley by Friday night with the NAM overall the weakest. A maintenance of the 00Z ECMWF/CMC preference remains for now. ...Shortwave trough digging across the Intermountain West... ...Energy amplifying into the Lower MS Valley by Saturday... ...Associated deepening surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z CMC/ECMWF and ECENS mean Confidence: Slightly below average A shortwave trough currently shifting east to the Pacific Northwest coast is forecast to take a southeast turn as it crosses the northern Rockies Thursday night and amplify across the southern Plains on Friday before crossing the lower MS Valley by Friday night and pushing into the Midwest Saturday. Guidance is in agreement on the trough becoming negatively tilted Friday night, driving another deepening surface low center. The 12Z NAM and 00Z UKMET become weaker outliers both at the surface and aloft with the system, with the main difference being that the UKMET is suggesting two low centers with over the lower MS Valley and one evolving over the Midwest (mentioned in the previous section) by Friday night given proximity of stronger northern stream shortwave energy lurking over the Midwest. The 12Z GFS remains too progressive by Friday/Saturday and probably takes its energy a bit too far north, but it has agreement with the UKMET in having stronger northern stream energy nearby. The difference between the UKMET and GFS remains that the GFS still has a more dominant southern stream shortwave trough and thus a dominant southern stream surface low. The 12Z GFS is still supported by the 00Z CMC and 00Z ECMWF solutions with the idea of there being one consolidated low evolving through the lower MS Valley by the end of the period and a more dominant southern stream trough, but that is where the agreement ends as the CMC/ECMWF camp is farther south and slower with the surface low evolution. The CMC/ECMWF camp is supported by the 00Z ECENS mean and somewhat by the 06Z GEFS. The preference will remain a blend of the slower CMC/ECMWF and ECENS mean. However, given some of the uncertainties over how strong the nearby northern stream energy and related interaction will be, confidence is a bit limited in the Friday/Saturday time frame. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson