Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 145 AM EST Sun Dec 01 2019 Valid Dec 01/0000 UTC thru Dec 04/1200 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: General model blend...through 48 hours 00Z GFS/12Z ECMWF/12Z ECENS blend...after 48 hours Confidence: Slightly above average The deep layered closed low crossing the Midwest will advance steadily east across the OH Valley on Sunday and reach the Mid-Atlantic region by Monday. The attendant area of low pressure will lift across the upper OH Valley and the lower Great Lakes region, with secondary cyclopedias occurring near the Delmarva by late Sunday which will then lift northeast and deepen near southeast New England through Monday. By Tuesday, the system should exit across the Gulf of Maine and reach Canadian maritimes. The guidance is in rather good agreement through about 48 hours, but thereafter, the 00Z GFS tends to focus is low pressure a little farther offshore of New England compared to the 00Z NAM, 00Z UKMET and especially the 00Z ECMWF. The ECMWF actually trended a bit farther west as the system arrives up across the Gulf of Maine. The 12Z CMC meanwhile is bit farther offshore as well, and actually is generally east of the GFS. Based on the latest trends and clustering, it would appear that the ECMWF my be a little too far west on Tuesday with its low placement, and also the NAM appearing to be too deep. Will prefer a general model blend through 48 hours, and then lean toward a blend of the 00Z GFS, yesterday's 12Z ECMWF and incorporating yesterday's 12Z ECENS mean. ...Upper low approaching the West Coast by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/18Z GEFS mean and 12Z ECENS mean Confidence: Average On 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 the guidance favoring a consolidation of the two systems offshore of California by Monday evening. The system is expected to drop south through Tuesday and then begin to advance southeast toward southern California by early Wednesday. The 00Z guidance has come into better agreement in taking the closed low a bit farther south compared to yesterday's 12Z/18Z cycles before the turn off to the southeast later in the period. The 00Z GFS and 00Z GEFS mean are a little northeast of the overall model consensus by the end of the period. Yesterday's 12Z ECENS mean though does still favor the latest GFS/GEFS camp, and so there is a tad of an uptick in uncertainty regarding the closed low placement as the 00Z UKMET/CMC and 00Z NAM solutions are a little bit farther south. For now, will maintain the earlier preference given the breadth of ensemble agreement. ...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 Monday and then drop it down across the OH Valley through Tuesday. The guidance is in good agreement through the period now as the 00Z UKMET has slowed its progression and is now in line with the model consensus. A general model blend will be preferred through the period as a result. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison