Of all the possible forms of severe weather during warmer months, large hail and lightning are among the most common.
Hail formation usually comes with isolated-cell or multicell thunderstorms. Freezing temperatures are required for hail to form, and formation depends on how far aloft the freezing line is located. The freezing line is closest to the surface in March and April, making hail more common in those months.
Tornadoes can happen at any time during the year, but are more likely in mid-May to early June, when there is just enough instability in the atmosphere and the jet stream is shifting north. That generates changing wind speeds and direction with height.
The classic structure of a supercell storm may have a flat updraft base and a wall cloud underneath its updraft. When the conditions are right, a tornado may form underneath the wall cloud. A classic cell will also have rotation, creating a hook when displayed on radar.
Severe storms can continue into the rest of June and July, when the warmer temperatures create more instability. This can create storms with stronger updrafts and downdrafts, the latter of which can cause damaging straight line winds.