Today, several tornado warnings were issued for supercells that moved across south central Ontario. They produced large hail and gusty winds.
The warm front currently draped over that region will move north into southern Quebec for tomorrow, and remain there on Canada Day. South of the front, substantial surface heating is expected, and dewpoints in the low 20s will accompany maxima in the mid 20s.
Low LCL heights and low-level helicity values over 100 m2/s2 and strong bulk shear over 40 kt will support organization of supercellular storms which may produce lowerings. Large hail is possible depending on the degree of destabilization and damaging wind gusts are also possible.
Updates to the situation on each day will likely be needed as some uncertainty remains present, especially regarding the degree of destabilization.
Decent upper level support will be present during this event as well, as shown on the 00Z RAP sounding for Ottawa for 5 pm tomorrow. Look at all of the marginal large hail analogues!