Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Tue Jun 16 2020 Valid Jun 16/1200 UTC thru Jun 20/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Southeast U.S. closed low and coastal front ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High The cut-off upper low that is currently parked over South Carolina is expected to remain nearly stationary through Wednesday evening before gradually lifting north and eventually becoming absorbed by the westerlies by the weekend. This is supporting a surface low near eastern North Carolina that is fueling convection and heavy rain for portions of the Southeast and Mid-Atlantic region. The models are indicating very good synoptic scale agreement on the progress of the upper level system. At the surface, the 12Z NAM is slightly weaker with the low, but still within the realm of possibilities. Therefore, a general model blend with high confidence can be recommended. Closed low moving into the Northwest Tuesday into the Northern High Plains by Thursday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Friday, then 12Z NAM/UKMET/ECMWF blend Confidence: Moderate The upper level low over Washington and Oregon Tuesday morning is forecast to cross the northern Rockies and become absorbed by a second evolving upper low over south-central Canada by Thursday. This will sustain an occluded surface low and a slow moving cold front across the Dakotas through the middle of the week. The two main differences noted in the guidance is a stronger system with the 12Z GFS across Saskatchewan and Manitoba, and the 12Z CMC becomes displaced to the south of the model consensus by 00Z Friday, although not to the same degree as the 00Z CMC run. Therefore a blend of the 12Z NAM/ECMWF/UKMET should suffice as a starting point in the forecast process. Trough approaching the Pacific Northwest by Friday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/GEFS mean/00Z EC mean Confidence: Limited-Moderate A shortwave trough pivoting around a broad upper level gyre over the Gulf of Alaska is expected to reach the offshore waters of the Pacific Northwest and Vancouver Island by Friday evening, accompanied by a slow moving cold front. The 12Z CMC is fastest in bringing this trough towards the British Columbia coast, and the NAM is more amplified by 6Z Friday and continues through 00Z Saturday. By the end of the forecast period Friday evening, the GFS and UKMET are both indicating a better defined low pressure wave on the front after the primary surface low passes through. Forecast confidence is limited by these differences, and therefore incorporating some of the ensemble means is prudent. Hamrick Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml