Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 230 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: 12Z GFS/12Z ECMWF 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. The 12Z UKMET has sped up its trough movement, when results in its solution being faster with the surface front as well. The faster solution makes the 12Z UKMET the fast outlier solution, and was dropped from the previous preference. Since there is still a fair amount of spread in how models are handling the short wave energy south of the closed mid level low, a 12Z GFS/12Z ECMWF (which can include their respective ensemble means) blend is preferred. 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