Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 253 PM EDT Sun Oct 06 2019 Valid Oct 06/1200 UTC thru Oct 10/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough crossing the Great Lakes through Monday... ...Attendant cold front moving into the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-ECMWF blend Confidence: Above average The models show very good agreement with the details of the upper trough and associated shortwave energy that will be crossing the upper Midwest and Great Lakes region through Monday. Although the 12Z ECMWF is a bit slower than the remaining model consensus as the energy crosses the Great Lakes and then northern New England Monday through Tuesday. An attendant cold front will cross the OH Valley and move toward the East Coast by Monday night and then offshore on Tuesday. A non-ECMWF blend will be preferred with this system. ...Shortwave energy amplifying over the Mid-Atlantic... ...Deepening surface low pressure off the East Coast... ...Weak surface low pressure impacting the FL Peninsula... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GEFS/00Z ECENS mean Confidence: Below average...except above average over FL The guidance again suggests secondary shortwave energy advancing across the mid-MS and OH Valleys that will break away from the westerlies and amplify toward the central Appalachians by later Monday and Tuesday, and with at least a weak mid-level closed low evolving near the northern Mid-Atlantic region by Wednesday. The 12Z NAM/GFS solutions are now overall the stronger cluster with respect to the height fall evolution, and the 12Z ECMWF with its weaker trend is now the weakest. The evolution of this weakness developing over the central Appalachians will be critical as there are indications this energy will interact with the northwest advance of a surface trough/tropical wave lifting northwest across the Bahamas and up off the East Coast. In fact, all of the models on the one hand suggest a weak low center crossing the northwest Bahamas and moving into south Florida by late Monday, with then an area of cyclogenesis occurring east of the Carolinas by Tuesday as the upstream height falls approach the East Coast. There is a fair amount of latitudinal spread in the guidance with where this secondary cyclogenesis will occur, but all of the models have collectively trended toward a low center tucking in closer to the Eastern Seaboard by Wednesday. One exception is the 12Z ECMWF which has trended farther offshore. The 12Z GFS is now overall the farthest west and north with the surface low center evolution through Wednesday, and is also west of the 12Z GEFS mean. The 12Z NAM/CMC solutions are a little southeast of the GFS, with now the 12Z UKMET/ECMWF solutions the farthest south, but with the ECMWF the farthest east. The GFS and ECMWF are now both appearing to be outlier solutions overall relative to the model consensus, although the ECMWF does at least have some support from the UKMET and 00Z ECENS mean. At this point, given the multi-day model swings and lack of strong clustering, the preference will be to lean toward a compromise of the ensemble means with the 12Z GEFS mean and 00Z ECENS mean. Confidence is limited with the offshore low center evolution, but is above average with respect to the separate low center impacting the FL Peninsula since the guidance shows much better agreement that feature. ...Deep upper trough/closed low amplifying over the West... ...High Plains cyclogenesis... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement on amplifying a northern stream trough down toward the Pacific Northwest, northern Rockies and northern High Plains by later Monday and Tuesday which will send a very strong cold front southeast from Canada along with much colder air. As the cold front advances southeast, one wave of low pressure will develop along it over southeast MT by late Tuesday which will cross the Dakotas through early Wednesday. The models show excellent agreement with this evolution. Then as the cold front advances down the Front Range of the Rockies by late Wednesday, a new area of strong cyclogenesis is expected to take place over eastern CO. Given the level of model agreement with the details of the frontal timing across the Great Basin and the High Plains, the pair of low centers, and the deep trough/closed low evolution expected over the Intermountain West, a general model blend will be preferred with above average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison