There will be a pretty substantial risk today in southern Alberta for a few supercells this afternoon. Watervapour imagery this afternoon (first image) shows a pretty large trough that is forecast to push into AB this afternoon, and has in fact began to do so as I’m writing this. This trough will begin to develop a low within the southern portion of the province where a warm front will begin to push northwards along with a weak cold front and stationary boundary setting up along the foothills (second image). The air along this boundary is forecast to see SBCAPE values well into the 1500-2000 J/kg range with up to 2500+ J/kg south of the warm front. Bulk shear values within the region are forecast to be 35-40 kt with 40-50 kt (third image) near the Medicine Hat region and forecast hodographs do indicate low level veering of the winds but mainly within a shallow layer. Thus there appears to be a broad risk are for convection (purple) but the pink region is where I think the greatest chance for supercells are. This region includes Calgary, south along QE2 to Lethbridge and region just to the west of the QE2, and over to Medicine Hat. The Medicine Hat region is lowest probability at the moment since there is a pretty strong CAP in place and storms may struggle some to get going. On top of that shear vectors more parallel to the warm front would suggest very messy type convection here. Furthermore forecast soundings in the region show that storms in this region will be rather elevated and thus render more of a strong damaging wind threat with some large hail.

The QE2 corridor from Lethbridge to Calgary is of peak interest this afternoon. Storms are forecast to fire along the foothills this afternoon, and satellite imagery is already indicating pretty decent cumulus development as that trough surges eastward. The strongly backed winds along with the veered wind profiles plus amble instability will likely be enough to get supercells. Veered profiles aren’t very deep but are such in the lowest levels that a brief tornado is possible. I expect storms will initiate within the next 2-3 hours with the most dangerous region being from Calgary-Lethbridge and along the QE2 corridor.