Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1230 PM EDT Wed Aug 05 2020 Valid Aug 05/1200 UTC thru Aug 09/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Long wave trough from the Great Lakes to the Gulf Coast... ...Closed mid level low over Ontario... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Both the 12Z NAM/GFS are close to the tight clustering taking the long wave trough extending from the Great Lakes to the Gulf Coast eastward, weakening it with time as the mid level ridging over the Atlantic slides to the east. While the 12Z GFS becomes a bit slower with the northern end of the trough over New England after 08/12Z, the difference is minor, and a general model blend is preferred with above average forecast confidence. ...Short wave crossing the Northern Plains/Upper Great Lakes... ...Energy lifting into the Northeast Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 12Z NAM/GFS are in lock step with the model consensus taking short wave energy over ND this afternoon across the Upper Great Lakes through 08/00Z, then tracking it across New England by 09/00Z. Considering the tight clustering with this feature, a general model blend is preferred with above average forecast confidence. ...Southern stream trough moving into CA... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Short wave energy over Northern CA this afternoon and evening drops into an evolving long wave trough forming over CA through 07/12Z. Additional short wave energy dropping into the back of the trough pulls the long wave trough axis just offshore of the CA coast. Eventually, the long wave trough weakens, possibly leaving an isolated closed mid level low off the southwest CA coast by 09/00Z. Once again, there is little spread in the model guidance in the development of the long wave trough (though there is some spread concerning the development of a closed mid level low this evening over Northern CA). With this in mind, a general model blend is preferred, with above average forecast confidence. ...Long wave trough crossing the Pacific Northwest... ...Closed low development over Saskatchewan/Manitoba... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 12Z NAM/GFS are close to the model consensus tracking a long wave trough across the Pacific Northwest by 07/00Z, which takes on a negative tilt as it reaches east central Alberta before 08/00Z. After this time, there is some model spread concerning the evolution of development of a closed mid level low over central Saskatchewan toward 08/12Z. The 12Z NAM/GFS are close to the consensus placing a closed mid level low over northern Manitoba (though the 12Z GFS does not keep the system closed). Only the 00Z CMC is noticeably slower than the consensus by the end of the period. While there is some model spread with the placement of the closed low by 09/00Z, the overall model agreement is close enough to support a multi model blend. The spread at the end of the cycle does however degrade forecast confidence a bit. ...Surface low development over the Central Plains Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average There is good model agreement with the development of surface low pressure over western KS/southwest NE after 08/12Z, though there is some spread within the individual 00Z ECMWF ensemble and 00Z GEFS members. From this distance, the spread appears to be be fairly negligible, so a general model blend is preferred with above 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 Hayes