Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1254 AM EDT Mon Aug 10 2020 Valid Aug 10/0000 UTC thru Aug 13/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Longwave troughing over the Northwest Tuesday-Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z GFS blend Confidence: Average As a broad mid-upper level trough axis translates eastward from the northeastern Pacific early this week, reaching southwestern Canada and the northwestern U.S. Tuesday into Wednesday. Of the latest guidance, only the 12Z GFS stands out with a slower progression of a shortwave into Washington and Oregon late Wednesday. For now, prefer to go toward the stronger consensus, outside of the 12Z GFS. ...Weak troughing/surface low along the southeastern U.S. coast on Wednesday. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS, 12Z ECMWF, 12Z UKMET blend Confidence: Below average Model forecasts take an existing MCV over the Lower Ohio Valley from Sunday morning, southeastward toward the Carolinas by Wednesday morning. The models differ in strength regarding this feature with most developing a surface low into the Southeast and near the coastline. The ensembles depict this feature rather well, and while single model is an outlier, the 12Z NAM is strongest and 12Z CMC lies on the eastern edge of the latest spread while also leaning toward the stronger side of the guidance. The 12Z GFS is weakest but a blend of the GFS with the 12Z ECMWF and 12Z UKMET appears to be the best compromise for this system. Confidence is low given the role of future convection in the evolution of this feature. ...Remainder of Overall weather pattern across the continental U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend led by the 12Z GFS and 12Z ECMWF Confidence: Average The remainder of the U.S. will feature quasi-zonal flow across the northern half of the nation with a bi-modal ridge centered over the Lower Mississippi Valley and southern Arizona/New Mexico. A large closed low will track east across Canada with some weakening through Wednesday. A cold front will follow at the surface with potential for convective flare ups near the frontal boundary. While differences exist with the models regarding these flare ups and their impacts on the mid-levels, no single model can be ruled out with any confidence. At this time, a general model blend is preferred but with the most weight toward the 12Z GFS and `1Z ECMWF as they are closer to the middle of the model spread with features across the remainder of the U.S., not already discussed in the above sections. There were no significant differences noted with the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. 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 Otto