Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 318 PM EDT Mon Jun 01 2020 Valid Jun 01/1200 UTC thru Jun 05/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Final Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper level low slowly lifting across west Texas and into Oklahoma through Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Moderate-High A broad upper low currently centered over northwest Texas will continue to slowly lift northward into Oklahoma tonight before weakening through Tuesday night east of broad upper ridge axis over the southern Rockies. All global guidance are in close enough agreement on the main features to merit the use of a multi-deterministic model blend. Developing low becoming cut-off and lingering west of Baja California through midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Moderate-High A developing upper level low will become pinched off from the westerlies farther north, and because of the ridge axis over the southern Rockies, it will wobble in place into Thursday before beginning to eject east toward the CA/Mexico border later Thursday. Placement and depth are in good enough agreement through Thursday among global deterministic guidance and a general model blend is recommended. One note is the 12Z UKMET and ECMWF are a bit deeper with the low center by late Thursday which may slow the eastern ejection of the low which is noted beyond the Day 3 timeframe with the GFS being more progressive. Active flow pattern across northern Tier of U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Moderate The westerlies on the northern periphery of the central U.S. ridge are expected to be rather active with four well defined shortwave disturbances tracking eastward near the U.S./Canada border through Thursday. The first shortwave, currently west of Lake Superior will track east-southeast across PA late tonight into Tuesday and produce a streak of precip from MI into PA tonight. The second wave is an occluded low moving into northern Manitoba which will weaken, but shift southeast with surface low pressure across northern NY state and southern New England Tuesday night. This will leave a cold front over the northeastern to north central CONUS which will be a focus for convective weather through Thursday. The third disturbance is a wave over BC which will track across the upper Canadian Prairies to Hudson Bay through Tuesday night which will leave a front near the Canadian border which will direct the next and fourth system which will reach the BC coast late Tuesday which will track just north of the border Wednesday and drag a cold front across the northern Great Plains Wednesday night. Weaker impulses from the north Pacific follow this fourth well-defined wave. There are essentially two camps with the position of the cold front over the Midwest Wednesday night/Thursday which is associated with the occluded low remnants that shift off the southern New England coast Tuesday night. The 12Z ECMWF/CMC agree on a farther north solution while the 12Z UKMET/GFS are slightly farther south with the 12Z NAM somewhat in between. Given the position of the front on Day 3 has an understandable difference, a general model blend is recommended. The 12Z CMC has come in better agreement with consensus with the progression of the last low tracking over the southern Canadian Prairies Wednesday/Wednesday night. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson