The National Weather Service in St. Louis has upgraded its previous heat advisory to an excessive heat warning now through Friday evening for the St. Louis area.

Dangerous heat is expected in the area beginning 11 a.m. Wednesday through 9 p.m. Friday, July 28 throughout the region.

Heat index values over 105 degrees are expected through Friday, with multiple locations forecasted to reach values between 110 and 115 in the afternoons and early evenings. The heat will ramp up Wednesday and peak Thursday and Friday afternoon. Hot temperatures and high humidity may cause heat illnesses.

The St. Louis County Office of Emergency Management encourages people to drink plenty of fluids and to stay in an air-conditioned room out of the sun if possible. Young children and pets should never be left unattended in vehicles under any circumstances.

Anyone who works outside should take extra precautions, and reschedule strenuous activities to the early morning or evening if possible. Wear lightweight and loose-fitting clothing. The Occupational Safety and Health Administration recommends frequent breaks in shaded or air conditioned environment.

Heat stroke is an emergency and 911 should be called in the event of suspected heat stroke.

Update Friday, July 28 at 4:30 p.m.: Although the heat warning and advisory will come to an end tonight, the National Weather Service in St. Louis advises that high heat index values will continue into Saturday. Severe thunderstorms are possible, mainly Saturday, with the primary threat damaging winds. Saturday’s heat index values are more uncertain due to projected cloud coverage, but could reach as high as 107 in parts of the St. Louis metro area.