Weather Alerts For Marissa, IL

# HEADLINE -------------------- EXTREME HEAT WATCH IN EFFECT FROM SUNDAY AFTERNOON THROUGH THURSDAY EVENING # DETAILS -------------------- WHAT Dangerously hot conditions with heat index values of 105 to 110 possible. WHERE In Illinois, Madison IL, Monroe IL, and Saint Clair IL Counties. In Missouri, Jefferson MO, Saint Charles MO, Saint Louis City MO, and Saint Louis MO Counties. WHEN From Sunday afternoon through Thursday evening. IMPACTS Heat related illnesses increase significantly during extreme heat and high humidity events. ISSUED AT Saturday, June 27, 2026 at 1:59 AM CDT ISSUED BY National Weather Service St Louis MO HEADER URGENT - WEATHER MESSAGE # PRECAUTIONARY/PREPAREDNESS ACTIONS -------------------- Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. # AREAS AFFECTED -------------------- Jefferson MO, Madison IL, Monroe IL, Saint Charles MO, Saint Clair IL, Saint Louis City MO, Saint Louis MO Including the cities of Saint Louis, Edwardsville, Cahokia, Saint Charles, Belleville, and Alton