There seems to be quite the excitement and buzz in the air as to what is in store weather wise for southern Manitoba tomorrow, and rightfully so. Latest water vapor imagery shows the potent upper trough sitting just on the western edge of Vancouver Island which will be the main focus for widespread large scale ascent over the northern U.S. Prairies/Canadian prairies tomorrow afternoon.
Starting aloft however for tomorrow, models (NAM-WRF/GEM/GFS) agree on a strong 250 mb jet nosing into the southeastern SK and southwestern MB through the afternoon/evening period and again at 500 mb same group of models indicating a strong jet axis into extreme southeaster SK and southwestern MB. Because of this scenario we end up with a deepening vorticity maxima aloft and enhanced large scale ascent across much of the prairies.
But this causes some issues now near the surface. With this rapidly deepening upper low, the surface low will occlude at a much faster pace thus leaving the possibility of having the warm sector pinched off before it even reaches the border. If this is the case then tomorrows severe weather potential goes virtually to 0. Current guidance however still indicates a warm front should extend from Winnipeg across to the ON/MN border just south of Thunder Bay. A cold front will extend from Winnipeg down through east central ND, into northwestern SD, and into northern CO. A trowal will then extend from Winnipeg up into north central SK around Prince Albert National park. The analysis was derived from the NAM/WRF 00Z surface forecast for Sunday June 10 (or the afternoon of June 9). Thus the southeastern corner of MB from Winnipeg to Kenora, ON and across the warm front boundary, a well as the portion of SK and MB which sit along the trowal are the focus areas for severe convective weather tomorrow afternoon. Note that both the GEM/GFS do have the triple point slightly north and west of the NAM/WRF, but given the rapid intensification of the upper low and vorticity center, I prefer the NAM/WRF solution here.
That being said, a quick look at the 500 mb chart above shows a ridge axis through eastern MB thus which may lead to some capping issues. Given 700 mb temps and CIN forecast, the cap will be breakable more the extreme southeastern portion of MB. Along the trowal however there is virtually no cap present, with 700 mb temperatures around the 3 to -1 degree C mark, thus there is a stronger potential for more vigorous convection with an even greater hail threat, but at the same time will make for a convective mess. Because of this there appears to be two regions of interest for strong tornadic thunderstorms tomorrow. A look at 850 mb flow and MLCAPE forecast will help reinforce the reasoning behind why this is. There are two main axis of strong low level flow indicated on the 850 mb forecast, the obvious axis through southeastern MB/northwester ON and the secondary axis through east central SK. The axis through SK appears to be a result of a secondary low spinning up along the trowal in response to strong cyclonic shear due to the 250+500 mb jets. In both areas forecast soundings indicate strongly veered hodographs thus rendering both the warm sector and areas along the trowal conducive to tornadoes. Thus two areas of focus for tomorrow where people should be aware and on the look out for severe weather: 1. Southern MB from Brandon across to northwestern ON along the Trans Canada and south along hwy 71. 2. From Portage la Prairie along hwy 16 northwest to Yorkton, SK and up to north-central SK to area east of Prince Albert National Park. Areas which I believe the most conducive to tornadoes are the Steinbach, MB area and regions just east of the Prince Albert National Park. Along with the tornadic threat is a large hail threat where greater than golf ball sized hail is possible for southeastern MB and up to golf ball sized hail possible for region in north central SK. Keep in mind however, these are regions I feel the worst could happen and that most of the people in MB and eastern SK need to be alert tomorrow since the entire region is prone to severe convective weather. That includes strong straightline winds, large hail, and tornadoes.
With current morning convection through MB looks as though the severe threat has diminished. Morning convection has generated a cold pool in the southern portions of the province thus hindering the northward progression of the warm front. Current model guidance does show the warm front eventually pushing into southern MB but HRRR keeps along the border with the RAP/RUC having the warm front pushing just south of the Trans Canada then east into Fort Frances. The cold front will drop south from Portage La Prairie into the Dakotas with a trowal extending from this location northwest into central SK. With CAPE still forecast to reach the upper 3000 j/kg range in southern MB there still exist a threat for isolated sever storms near the triple point and then back along the trowal. The tornado threat has sharply decreased because of the morning convection and will depend on whether or not the warm front can push into MB. If so then there will be a marginal tornado risk for areas just south and east of Winnipeg across the Trans Canada to hwy 71 just east of Lake of the Woods and south to the U.S. border. But there is still a severe threat for the areas outlined in yesterdays discussion for strong winds and large hail.