ILLINOIS — Tomorrow is shaping up to be the hottest day of the year by air temperature in southern Illinois, with actual air temperatures forecast near or at 100 degrees in many spots. This marks a significant peak in the summer heat, with triple-digit readings expected across a wide stretch of the region.

St. Louis and Paducah Both Forecast to Hit the Century Mark

St. Louis is forecast to reach 100 degrees, tying for the hottest reading across the broader region alongside Paducah, Kentucky, which is also expected to hit exactly 100 degrees. These two metro areas represent the most significant heat concentration on the forecast map.

Nearby, Cape Girardeau is forecast to reach 99 degrees, while Poplar Bluff, Missouri, could see the hottest reading of all at 101 degrees, illustrating how widespread the extreme heat is expected to be across the greater Mississippi Valley region.

Mid to High Nineties Expected Across Much of Southern Illinois

A broad swath of southern Illinois communities, including Mount Vernon at 98 degrees, Harrisburg at 96 degrees, and Farmington at 98 degrees, fall into the mid to high 90s range. This represents dangerously hot conditions even without factoring in humidity-driven heat index values.

Vincennes and Princeton, just across the Indiana border, are also forecast to reach 96 degrees, showing the heat extending well beyond Illinois into neighboring states as the same broad area of hot air mass settles over the region.

Northern Edge of Heat Dome Shows Cooler Readings Near Terre Haute

While most of the region faces extreme heat, the northeastern edge of the forecast area shows a notable drop-off, with Charleston forecast at a much cooler 84 degrees and Terre Haute at 83 degrees. This sharp contrast illustrates the northern boundary of the most intense heat.

Effingham, positioned between the hottest core and this cooler northern fringe, is forecast to reach 90 degrees, representing a transition zone between the two temperature regimes across central and southern Illinois.

Evansville and Western Kentucky Also Face Triple Digit Heat Index Potential

Evansville, Indiana, is forecast to reach 98 degrees, while Madisonville and Hopkinsville in western Kentucky are expected to see readings of 96 and 98 degrees respectively, extending the extreme heat well into the Ohio Valley and western Kentucky region.

Residents across southern Illinois, eastern Missouri, and the surrounding tri-state region are urged to take heat safety precautions Friday, including limiting outdoor activity during peak afternoon hours and staying hydrated as temperatures approach or reach the century mark.