Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1217 AM EDT Wed Jun 3 2020 Valid Jun 3/0000 UTC thru Jun 6/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper level low slowly lifting into Oklahoma that drifts east into Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Moderate-High A broad upper low currently centered over eastern Oklahoma will track eastward across Arkansas, and then evolve into a broad upper level trough. The 250-500 mb trough axis will extend southward over the northern Gulf of Mexico, and this will be important since upper level flow ahead of it will play a role in the future track of Tropical Storm Christobal. All global guidance are in close enough agreement on the main features to merit the use of a multi-deterministic model blend. Cut-off low lingering southwest of California through Thursday before ejecting east ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Friday, then non-GFS Day 3. Confidence: Moderate-High A cut off upper low will remain nearly anchored in place through Thursday west of the ridge axis over the southern Rockies before beginning to eject east toward southern California by Thursday night and into Friday. Similar to yesterday, the GFS remains slightly faster in bringing the closed low eastward on Friday compared to the other guidance, and therefore the preference for Day 3 is non-GFS at this time. Active flow pattern across northern Tier of U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend through Thursday, then 12Z ECMWF/UKMET/EC mean Confidence: Moderate The westerlies on the northern periphery of the central U.S. ridge will remain active with two well-defined shortwave disturbances tracking eastward near the U.S./Canada border through the end of the week. The first disturbance is a shortwave over northern Manitoba which will track south of the Hudson Bay by Wednesday and be directed across northern Maine by a deep low over Labrador, and result in a cold front stalling over the east-central U.S. and provide a focus for rainfall. The second system, currently over Alberta, will track just north of the border and evolve into an upper low over Manitoba by Wednesday night. This will send a cold front across the northern Great Plains Wednesday night and across the Midwest by Thursday. Despite the quasi-zonal and progressive flow pattern in place across the region, models are in good agreement through Thursday, except for the 12Z CMC which slowed from the 00Z run, but more importantly flatter than the rest of the guidance with eastward progression of the second wave over the Canadian Prairies starting late Wednesday. The 00Z GFS becomes slightly more amplified with the second wave by Thursday evening across the northern Plains, and the NAM is slower with it by Friday as it crosses the northern Great Lakes region. Closed low drifting south from Gulf of Alaska by Friday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Friday, then non-CMC blend Confidence: Moderate-High An upper level low originating over the Gulf of Alaska is expected to drop southeastward, west of the British Columbia coast, and be situated several hundred miles west of the Washington coast by Saturday morning. Except for a slightly slower 12Z CMC beyond Friday morning, there is enough deterministic model agreement to merit the use of a general model blend for this region. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick