Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1243 AM EDT Sun May 19 2019 Valid May 19/0000 UTC thru May 22/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/surface low crossing the Midwest/Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average The models all take the relatively deep upper trough currently over the central/northern Plains off to the northeast across the Midwest on Sunday and then the Great Lakes region by Monday. This will allow surface low pressure to cross these areas before gradually ejecting into southeast Canada on Monday. The 00Z NAM appears to be too weak with its surface low through the period. The 00Z GFS may be potentially a tad too progressive, but there is some ensemble support from the GEFS suite of guidance. Meanwhile, the 12Z non-NCEP guidance is collectively a tad slower than the NAM and GFS. For now, will suggest a non-NAM blend. ...Deep closed low crossing the Southwest through Monday.... ...Going negative tilt across the High Plains by Tuesday... ...Leeside cyclogenesis over the High Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours Blend of the 00Z GFS/12Z ECMWF...after 36 hours Confidence: Average The latest guidance brings a strong closed low and associated trough in across CA through Sunday, with the height falls then digging vigorously southeastward across the Southwest and the Four Corners region through Monday. In fact, the height falls will be quite anomalous for the time of the year, and running about 3 to 4 standard deviations below normal. This will generate strong cyclogenesis initially over the southern High Plains on Monday in vicinity of a well-defined frontal zone, and this low center will quickly deepen through Tuesday and begin lifting north toward the Dakotas as the upstream upper trough/closed low takes on a negative tilt as it ejects out across the High Plains. Through 36 hours, the models are in good agreement with the height fall evolution, but thereafter the 12Z UKMET begins to trend on the slow side of the guidance in ejecting the energy out across the High Plains. Its surface low in the lee of the Rockies is initially well south of the remaining guidance as well. The 00Z NAM for its part appears to be too weak with the surface low evolution. There overall appears to be better ensemble support for a 00Z GFS and 12Z ECMWF compromise, and so a blend of these solutions will be preferred for the time being. ...Vigorous Pacific closed low digging into the West Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/12Z ECMWF Confidence: Average There will be yet another strong northern stream closed low feature that will cross portions of the Pacific Northwest by early Tuesday and then dig sharply into the Intermountain West by late Tuesday on the heels of the initial deep closed low feature crossing the Southwest on Monday. This next system will help yield a very large area of below normal heights across the Western U.S. by Wednesday. The 00Z GFS, and especially the 00Z NAM are on the faster side of the guidance with this system, versus the slower 12Z non-NCEP guidance. The ensemble suites are generally split, with the GEFS favoring the faster camp, and the ECENS/CMCE favoring the slower solutions. For now, a compromise between the faster and slower camps will be preferred by recommending a 00Z GFS/12Z ECMWF blend. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison