Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 109 PM EDT Wed Aug 12 2020 Valid Aug 12/1200 UTC thru Aug 16/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Longwave trough over the Northwest to the Northern Plains through Friday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: NAM/CMC/ECMWF blend Confidence: Slightly above average A broad upper level trough, in conjunction with a closed low over southwestern Canada and a closed mid- and upper-level high along 155W, will be in place across the northwestern U.S. through the middle of the week. Overall, the models are in agreement with the idea that the trough gradually shifts eastward and be in place across the northern Plains by the weekend. This will sustain a cold front tracking from the northern Rockies to the Dakotas. The 12/12Z GFS becomes faster and more amplified with this trough by 12Z Friday across the Dakotas than the 12/00Z runs of the UKMET and ECMWF which is a typical bias of the GFS. Will continue to favor a blend of the 12/12Z NAM and 12/00Z CMC/ECMWF preference. Northeastern U.S. upper trough ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECMWF/CMC blend Confidence: Average An upper level trough axis gradually builds in across New England and eastern Canada by the end of the week, downstream of a building ridge axis across Ontario and western Quebec. The latest NAM was the strongest with the trough, while the GFS was slightly east of the model consensus. Blending the ECMWF and CMC would still yield a suitable starting point in the process process. Southeastern U.S. upper trough ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12/00Z ECMWF Confidence: Below average A weak closed low currently over Missouri will slowly track eastward and evolve into an open trough as it reaches the Ohio Valley and southern Appalachians by this weekend. The models have a better handle on the evolution of the flow pattern aloft but some rather large differences develop at 850 mb and...to a lesser extent...at 700 mb with respect to where a closed low forms. The ECMWF favored a low over Alabama while the GFS was north of the Ohio River by Saturday morning. Given the range of solutions will tend to prefer the ECMWF solution overall but with below average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Bann