The National Weather Service in Paducah has issued an Extreme Heat Warning for Southern Illinois from 11am today (Thursday) through 8pm Sunday.
Dangerously hot conditions are expected throughout the period, with daily heat index values reaching between 105 and 110 degrees.
Forecasters say little relief is expected overnight, with low temperatures only falling into the mid to upper 70s. The prolonged heatwave is expected to be the longest of the summer season so far.
The National Weather Service warns that the combination of extreme heat and high humidity will significantly increase the risk of heat-related illnesses.
Residents are urged to drink plenty of water, limit time in the sun, spend time in air-conditioned locations and check on relatives, neighbors and pets. Those who must be outdoors should take frequent breaks.