Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 101 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 Initial Model Evaluation Including Final 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 west Texas will continue to slowly lift northward into Oklahoma through Tuesday evening before weakening as it enters the broad upper ridge axis across the Mid-South by Wednesday. 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 excellent agreement through Thursday among global deterministic guidance and a general model blend is recommended. Active flow pattern across northern Tier of U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC General Model Blend Confidence: Moderate-High 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. Models are all in excellent agreement with the first three waves which mainly affect the Day 1 and 1.5 (through Tuesday night) forecast. The 00Z CMC is too fast and weak with the last wave once it pushes onto the southern Canadian Prairies on Wednesday. The 00Z ECMWF/UKMET and 12Z GFS/NAM are all in good enough strength and position with this low that they can be used as good references for this system which is the dominant Day 2/3 system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson