Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 233 PM EDT Sat Sep 01 2018 Valid Sep 01/1200 UTC thru Sep 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...with final preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Synoptic Pattern across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...led by 12Z GFS/12Z ECMWF Confidence: Average Across the lower 48, ridging will remain over the Mid-Atlantic region with mean troughing over the western U.S. through Tuesday. Across the Gulf of Mexico, a couple of easterly waves are expected to track west, one currently along the central Gulf Coast and a second across Florida on Monday. Up north, there is generally good agreement with timing of shortwaves and placement of a frontal boundary extending through the Great Lakes into the upper Midwest. Another cold front is forecast to reach the northern Plains on Tuesday, meeting up with the tail end of the upper Midwest boundary. Mass field differences are relatively minor with these systems, with a blend of the 12Z GFS/12Z ECMWF a decent compromise of the smaller scale differences. Across the Gulf of Mexico, the 12Z NAM stands out with hanging back the 1st wave along the western Gulf Coast on Monday into Tuesday while the remaining consensus takes the mid-level energy north into the southern Plains. Not going with the 12Z NAM across the Gulf is preferred given a lack of support for its solution. The second wave near Florida for early in the week shows some placement and timing differences with the mean position in the guidance nearest to a blend of the 12Z GFS/12Z ECMWF. Note that only minor changes were noted between the 12Z ECMWF/UKMET/CMC compared to their 00Z cycles. The 12Z ECMWF is much stronger compared to the 12Z GFS, but a blend of position and strength is preferred at this time with ensemble scatter low plots showing some weak support for a defined low, similar to the 00Z/12Z ECMWF. The NHC is highlighting a 40 percent chance of tropical cyclone formation for this system through the middle of next week, so please refer to NHC products for the latest updates on this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto