Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 139 AM EST Sat Nov 30 2019 Valid Nov 30/0000 UTC thru Dec 03/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low crossing the Intermountain West/Plains... ...System reaching the Mid-Atlantic/New England by Mon/Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend...through 60 hours Non-NAM blend...led by 00Z GFS/ECMWF...after 60 hours Confidence: Slightly above average The deep layered closed low currently moving through the Intermountain West will reorganize and deepen across the High Plains and Midwest on Saturday along with development of a notably strong surface low. Thereafter, the system advances east across the OH Valley and reaches the Mid-Atlantic region by Monday, with the attendant area of surface low pressure redeveloping along the Mid-Atlantic coast and lifting northeast near southeast New England by early Tuesday. The 00Z CMC appears to be a tad too weak with the system as it crosses the Plains and Midwest, but does come into better agreement with the model consensus as it arrives along the East Coast. The 00Z NAM by Monday and Tuesday appears to be a little too deep with its mid-level low center over the Mid-Atlantic and southeast New England. Meanwhile, toward the end of the period, the 00Z UKMET may be a tad slow. The spread seen earlier between the GFS and ECMWF late in the period has narrowed considerably with the 00Z cycle, and there is good ensemble support for this cluster with respect to both the low and mid-level low placements. The latest GEFS mean and ECENS mean support the GFS/ECMWF camp. So, based on the latest model trends and clustering, a non-CMC blend will be preferred through 60 hours, followed by a non-NAM blend led by the 00Z GFS/ECMWF after 60 hours. ...Upper low approaching the West Coast by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GEFS mean/12Z ECENS mean Confidence: Average By Sunday, a new closed low will be evolving offshore of the West Coast, including a separate center over the Northwest U.S. which breaks away and pivots offshore the West Coast. There will be some binary interaction between the two centers, with most of the guidance favoring a gradual consolidation of the two systems. Most of the guidance suggests this consolidated system then dropping south offshore CA through Monday and Tuesday. The 00Z NAM/GFS and 00Z CMC appear to be possibly placing the mid-level low center too far north by the end of the period, as the 00Z UKMET/ECMWF and the latest GEFS mean and ECENS mean favor the system focusing a little bit farther south. Will favor the latter camp with an emphasis on the ensemble means. ...Shortwave approaching the Northern Plains/Upper Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models bring a northern stream shortwave southeast across portions of the northern Plains and upper Midwest by the end of the period along with a new cold front. There is sufficient model mass field agreement with this system to favor a general model blend at this point. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison