Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 301 AM EDT Sun Sep 02 2018 Valid Sep 02/0000 UTC thru Sep 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation...with latest preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Synoptic Pattern across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/00Z ECMWF...across the CONUS 00Z GFS/00Z ECMWF/12Z ECENS mean blend...Gulf Coast Confidence: Average Ridging over much of the Eastern U.S. will remain in place going through Wednesday, and the guidance again agrees strongly that the subtropical ridge will strengthen with time over the Mid-Atlantic region going through the middle of the week. Meanwhile, a mean layer upper trough is expected to remain intact over the Northwest U.S. as northern shortwave energy continues to reinforce height falls across the region at least through Tuesday. On Wednesday, the troughing over the Northwest does begin to lift out though as height falls offshore of British Columbia allow a shortwave ridge to advance inland. Meanwhile, there will also be a broad southern stream weakness/trough focused over the Four Corners region which will tend to retrograde westward a bit by the middle of the week. Key features of note through the period will again be the ejection of small scale vort centers/shortwaves that will be lifting north and northeast around the western and northern periphery of the aforementioned subtropical ridge over the Eastern U.S. and interacting with a well-defined frontal zone over portions of the central Plains and the Midwest which will also be influenced by the northern stream energy crossing the Pacific Northwest and northern High Plains. By Wednesday, this front will make at least some attempt to drop farther southeast as there will be somewhat stronger height falls crossing southern Canada. On the large scale, the dynamical guidance is in good agreement with their mass fields, although the 00Z CMC did exhibit a stronger low pressure wave lifting northeast up along the front involving the upper Midwest by early Tuesday. The 00Z NAM also tends to have some wave activity a tad out of tolerance as compared to the 00Z GFS/00Z UKMET and 00Z ECMWF. However, regarding the ECMWF, it may be just a tad too strong with its wave of low pressure lifting up across northern IA and southeast MN Tuesday night and early Wednesday. Otherwise, at this point, the GFS and ECMWF tend to have the best model clustering, and so a blend of the GFS and ECMWF will still be preferred across the CONUS. Regarding the tropical wave and possible low development over the northern Gulf of Mexico by Tuesday, the 00Z UKMET, 00Z CMC and 00Z ECMWF have all clustered much better with each other in suggesting a developing low center which will be approaching south-central to southeast LA by 12Z Wednesday. The 00Z NAM is the weakest solution and supports generally nothing more than a wave axis at the same time. The 00Z GFS is in between the stronger and weaker camps. The key trend of the ECMWF this cycle was to trend weaker, albeit still stronger then the GFS, but it is very close to the 12Z ECENS mean with depth and its track forecast has been very consistent run to run. As of this cycle, the UKMET and CMC are the strongest solutions. Thus, based on the latest model trends and clustering, the preference will be for a developing surface low approaching southeast LA by 12Z Wednesday, with a preference toward a blend of the 00Z GFS/00Z ECMWF and 12Z ECENS mean blend. Please consult the latest TWOAT from the NHC for more details 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 Orrison