Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 AM EDT Tue Jun 02 2020 Valid Jun 02/0000 UTC thru Jun 05/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Initial Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper level trough exiting the Northeast U.S. on Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High A pronounced upper level trough by early June standards will be in place across the northeastern U.S. on Tuesday before lifting out across eastern Canada as the upper level flow pattern becomes more zonal and the airmass warms up substantially. Although there are some minor differences once the trough reaches eastern Canada, there is excellent agreement for the Northeast U.S. through Tuesday before the trough lifts out, so a general model blend can be recommended. 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 western Texas will continue to slowly lift northeastward across Oklahoma through Tuesday night, and then gradually weaken over Arkansas as it becomes embedded in the broad upper level ridge. All global guidance are in close enough agreement on the main features to merit the use of a multi-deterministic model blend. Developing cut-off low lingering southwest of California through midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/12Z ECMWF/12Z UKMET Confidence: Moderate-High A broad upper low has become pinched off from the westerlies farther north, and because of the ridge axis over the southern Rockies, it should remain nearly anchored in place through Thursday before beginning to eject slowly east toward southern California by Friday morning. Similar to last night, the ECMWF ensemble members are generally a little to the west than most of the GEFS ensemble members. By Friday morning, the GFS and the GEFS mean are the quickest to progress the low eastward. The 12Z UKMET lies near the middle of the ensemble spread and represents a good choice in terms of model choices, along with some of the ECMWF and NAM. Active flow pattern across northern Tier of U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/12Z UKMET/12Z EC mean Confidence: Moderate The westerlies on the northern periphery of the central U.S. ridge are expected to be rather active with three well defined shortwave disturbances tracking eastward near the U.S./Canada border through mid-week. The first system is an occluded low moving across Ontario and Quebec that will gradually weaken, and bring a strong warm front surging eastward towards the East Coast by Tuesday night and early Wednesday. The second disturbance is a shortwave over Montana and Alberta which will track across south-central Canada to the Hudson Bay by Wednesday morning, which will leave a front near the Canadian border that will direct the next and third system reaching the British Columbia coast late Tuesday which will track just north of the border and evolve into an upper low over Manitoba by Thursday. This will support a cold front across the northern Great Plains Wednesday night. Given the quasi-zonal and progressive flow pattern in place across the region, this is where the greatest model differences currently exist, mainly with the second and third systems. Both the 18Z and 00Z GFS have been more suppressed with the upper level height pattern across the northern tier states compared to the other guidance, and near the southern extent of the ensemble member spread. By Thursday morning, the ECMWF and the CMC become faster with the upper low reaching Manitoba, and the ECMWF is also ahead of its ensemble mean. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick