May is warm in late spring in Illinois but prone to occasional bouts of heavy rain. The average high temperatures are in the beautiful 68°F (20°C) to 78°F (25.6°C) range, while the nights are comfortable between 46°F (7.8°C) to 57°F (13.9°C). Marion in the south averages in the warm 54°F (12.2°C) to 74°F (23.3°C) range, while Antioch in the north is between 47°F (8.3°C) to 68°F (20°C) and Quincy in the center ranges between 53°F (11.7°C) to 73°F (22.8°C). The last remnants of snow disappear from the ground as substantial rainfall to the tune of 5" (127mm) to 6" (152mm) occurs in many parts, especially in the south. Tourist numbers swarm in the state parks as the conditions are warm in the absence of cold waves. The skies quickly transition from sunny to cloudy, and heavy rain catches tourists by surprise. The season of thunderstorms and tornadoes begins and often brings severe bouts of weather. Expect occasional spells of heavy rain along with occasional hail. Spring is the time for scenic drives in the breezy atmosphere of May in Illinois.