Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1246 PM EDT Sun Jun 28 2020 Valid Jun 28/1200 UTC thru Jul 2/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low anchored over New England ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average An upper-level low initially over southern Quebec is forecast to reach central New England by Monday and then become anchored in place through the middle of the week as it becomes cut off from the main northern stream flow. The models have trended closer to a tight consensus regarding this low/trough, with the CMC only slightly displaced to the northeast with the core of the upper low. However, the difference is small enough to merit a general model blend for the Northeast U.S. Deep upper trough/closed low across the Intermountain West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/00Z UKMET/ECMWF Confidence: Average A strong mid-upper level low currently over the Pacific Northwest is forecast to continue amplifying across the northern Rockies and Intermountain West through Tuesday morning as an upper-level ridge builds across the Midwest and Great Lakes region, and then the core of the upper low should be centered over southwest Canada by Wednesday. This will yield a quasi omega-block pattern across the north-central U.S. through the middle of the week. The 12Z NAM tends to lift the trough out faster than the other guidance, and therefore the surface low over Alberta is displaced to the north. The 00Z CMC is slower with the trough evolution and lags the remaining model suite as the energy pivots through the Intermountain Region, resulting in a southeastward displacement of the mid-level low center. The 12Z GFS, 00Z UKMET and 00Z ECMWF have some modest timing/depth differences but overall are well clustered and represent the model consensus, so a blend of those models should work well. Shortwave lifting from the western High Plains to the Upper Midwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z UKMET/ECMWF blend Confidence: Average Ahead of the deep western U.S. trough/closed low will be a shortwave perturbation that ejects northeast out across the Plains and Midwest. The shortwave that is currently over western Kansas is forecast to track northeastward to the Upper Midwest and amplify into possibly a weak closed low over western Ontario as suggested by the 12Z NAM, as some modest energy lifting northeast in behind it merges and consolidates with it, and there has been a gradual trend to a stronger shortwave in the guidance. This also holds true with the 12Z GFS. Given the trend to a stronger solution, a blend of the GFS/NAM/ECMWF should suffice as a starting point. Shortwave crossing the Rio Grande Valley on Sunday Amplifying toward mid MS Valley by Monday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Average The guidance supports a convectively enhanced shortwave or MCV lifting northeast across the lower/middle Rio Grande Valley on Sunday which is forecast to lift northeast toward the Mid-South by Monday night while attempting to amplify. The models all appear to be trending stronger with this feature overall, and support a weak mid-level low center impacting the general vicinity of southern Illinois by Tuesday morning, with this feature most evident at 700 mb. One of the main differences noted was a stronger CMC solution across the Ohio Valley by Wednesday, whereas the other models are suggesting a slightly weaker low that is farther north. For now, a non-CMC 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 Hamrick