Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1229 PM EDT Thu Jul 16 2020 Valid Jul 16/1200 UTC thru Jul 20/0000 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 crossing the north central US into eastern Canada through Fri with an accompanying surface cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 12Z NAM/GFS are close to the consensus with both the mid level trough and its attendant surface cold front crossing the Northeast Fri (though the 12Z GFS could be a bit fast with the frontal passage on the East Coast). Based on the good clustering in the mid level and at the surface, a general model blend is preferred with slightly above average confidence. ...Cut off low west of California through Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Both the 12Z NAM/GFS are clustered well with the consensus taking the mid level system just off the Southern CA coast today and tracking it westward into the Pacific under the broad mid level ridge extending across much of the southern portions of the US. Given the tight clustering, a general model blend is preferred with above average forecast confidence. ...Long wave trough crossing the Pacific Northwest today, moving into south central Canada by Sat, then clipping the Northern Plains into Upper Great Lakes by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-12Z NAM blend Confidence: Average The 12Z NAM/GFS are close to the model consensus taking the long wave trough from the Pacific Northwest and British Columbia and closing off a mid level system over Manitoba near 19/00Z. After that time, the 12Z NAM becomes deeper and slower with the short wave energy south of the closed low across the Northern Plains into the Upper Great Lakes, particularly during Day 3. The deeper/slower short wave energy allows the 12Z NAM to develop a deeper surface low on a front extending across the area (something the NAM does often in this situation). Based on this, the 12Z NAM was not included in the model preference. During Day 3, because of the fast mid level flow south of the closed mid level low, the timing of the short waves become more nebulous with time. While a general model blend should suffice, perhaps using the 00Z GEFS mean and 00Z ECMWF ensemble mean could dampen some of the differences in the timing in the fast flow. Because of the subtle differences in the short wave timing, the forecast confidence is only average. 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