Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1156 PM EST Sat Nov 30 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 NAM/GFS and 12Z ECMWF 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 and 12Z ECMWF. The 12Z CMC tends to be a bit farther offshore as well, but the 12Z UKMET is farther west and left of the NAM/ECMWF camp with the primary low center. Toward the end of the period, the GFS has trended a little more favorably toward the NAM/ECMWF cluster with this cycle. So, based on the latest trends and clustering, a general model blend will be preferred through 48 hours, followed by a NAM/GFS and ECMWF blend thereafter. ...Upper low approaching the West Coast by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/18Z GEFS mean and 12Z ECENS mean Confidence: Slightly above 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 12Z CMC does not drop the closed low as far south as the remaining guidance, and by the end of the period, the CMC is also a bit quicker to edge the system toward southern California. The 00Z NAM and 12Z ECMWF are both on the southwest edge of the deterministic model spread, and a little southwest of the latest GEFS mean and ECENS mean which both are supportive of the 00Z GFS. Will favor the GFS-led consensus and the ensemble means with this system for the time being. ...Shortwave approaching the Northern Plains/Upper Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours Non-UKMET blend...after 48 hours 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 48 hours, but thereafter the 12Z UKMET begins to outrun the remaining guidance with the timing of its height falls. Will prefer general model blend through 48 hours, and a non-UKMET blend thereafter. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison