Severe thunderstorms taking on supercellular characteristics will form across eastern Ontario and southern Quebec late this afternoon and early this evening.

Most severe weather hazards are possible – hail up to 5 cm in diameter, wind gusts in excess of 100 km/h, as well as a few tornadoes. Fast storm motion and PWATs under 38 mm should reduce rainfall totals to relatively minor amounts.

MUCAPE over 2500 j/kg and effective bulk shear over 60 kt will create a very favourable environment for discrete supercells. 0-1 km helicity over 300 m2/s2 and LCL heights up to only 1 km will allow for tornado potential, and WBZ heights of just under 3 km should allow for a favourable environment for large hail. DCAPE values over 1000 j/kg and 90 km/h winds just 1 km AGL will undoubtedly produce damaging wind gusts at the surface.

Many areas could see more than one round of convection today, especially in central Quebec.

One unusual atmospheric quirk seems to be that most models have a dry intrusion at 700 and 850 mb move through the St. Lawrence Valley this evening, which kills all storms approaching it. However, some models do have the low levels moistening up with favourable parameters but storms still weaken while approaching the region. I do not believe that this will happen as there are no documented cases of storms weakening just due to the presence of the St. Lawrence Valley. They shoul

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