Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Thu May 24 2018 Valid May 24/1200 UTC thru May 28/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS evaluation including initial preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low development over the Gulf of Mexico into Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00z ECMWF/CMC blend Confidence: Average Both the 12Z NAM/GFS are close to the model consensus early concerning the tropical wave off the Yucatan Peninsula late Thu morning as it tracks northward ahead of a strengthening mid level ridge over the western Gulf of Mexico. However, the 12Z NAM slows with time with the surface feature (as well as its mid level circulation), and by Sun evening becomes much slower and further west with the surface wave. The 12Z GFS, in contrast, remained much more consistent with its track of the surface system, maintaining a slower and further west track over the last three cycles. This places the 12Z GFS very close to the 00z ECMWF/00Z ECMWF ensemble mean by Sun evening. The 00Z CMC is also close to the this position, while the 00Z UKMET remains the eastward outlier with the surface and mid level system (as its mid level ridging over the eastern Caribbean is further east than the consensus. Since the 12Z GFS is close to the 00Z ECMWF/00z CMC with the surface low, these solutions comprise the favored blend. Because of the 12Z NAM and 00Z UKMET maintaining seemingly outlier positions, the forecast confidence remains average. ...Shortwave and surface wave clipping New England late Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average confidence Both the 12Z NAM/GFS are close to the consensus with the short wave energy crossing Ontario/Quebec late Fri into Sat. These solutions are also close to the consensus concerning weak surface lows that develop on a frontal boundary extending from the northern Mid Atlantic states across southern New England, as surface high pressure crossing northern New England. Given the good model clustering with these systems, a general model blend is preferred with above average confidence. ...Short waves tracking across the Northern Rockies along the Canadian border Sat/Sun ...Associated surface low across Great Lakes Sat/Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z UKMET blend Confidence: Slightly above average Both the 12Z NAM/GFS are in close agreement with the short wave energy over Alberta/Saskatchewan Thu afternoon, and remain close to the consensus as the short waves cross the upper Great Lakes sat into Sun. Only the 00Z UKMET is slower than the consensus at this point with the short wave, as it becomes deeper and slower with the short wave over the UP of MI. Interestingly, the 00Z UKMET is not far from the consensus (held by the 12Z NAM/GFS) with the surface wave that crosses MN/WI/UP of MI during this time frame. However, the slower timing of the 00z UKMET does result in some differences in mass fields over the upper Great lakes, so this solution was excluded from the blend. ...Closed low off central West Coast reaches CA by early Fri before closing off over the Great Basin by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Both the 12Z NAM/GFS are closer to the model consensus as they close off a mid level low at the base of a long wave trough late Thu into early Fri. After that time, there is very good model agreement as the closed mid level low comes ashore over central CA Fri afternoon, then crosses the Great Basin Fri night into Sat night. Given the very good clustering of the operational/ensemble means with the mid level system, a general model blend was preferred with above average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes