Cities across the Midwest and eastern U.S. braced Sunday for another day of dangerously hot temperatures as a rare June heat wave continued to grip a portion of the country.

The temperature had already reached 80 degrees Fahrenheit (26.6 degrees Celsius) in the Chicago area by 7:30 a.m. Sunday, according to the National Weather Service. Forecasts called for heat indices of between 100 and 105 degrees F (37.7 to 40.5 degrees C).

The heat index in Pittsburgh was expected to top 105 degrees F. The temperature in Columbus, Ohio, was 77 degrees Fahrenheit (25 degrees Celsius) at 8:30 a.m. Highs there were expected to reach 97 degrees F (36 degrees C) with a heat index around 104 degrees F (40 degrees C).

Sunday marked the second straight day of extreme heat across the Midwest and East Coast. Heat indices on Saturday hit 103 degrees F (39.4 degrees C) in Chicago and 101 degrees F (38.3 degrees C) in Madison, Wisconsin, turning that city’s annual naked bike ride into a sticky and sweaty affair. Minneapolis baked under a heat index of 106 degrees F (41.1 degrees C).

The heat is expected to persist into the coming week, with the hottest temperatures shifting eastward. New York City is expected to see highs around 95 degrees F (35 degrees C) on Monday and Tuesday. Boston is on track for highs approaching 100 degrees Fahrenheit (37.7 degrees Celsius) on Tuesday, and temperatures in Washington, D.C., were expected to hit 100 degrees F on Tuesday and Wednesday.