According to an alert sent out by the National Weather Service, a heat advisory is in effect for St Louis County, St Charles County and the City of St Louis from 12 p.m. Tuesday to 7 p.m. Saturday.
The NWS advisory included the following warning and states the following conditions are expected.
High temperatures each afternoon will peak in the mid to uppers 90s with heat index values around 100. These levels of heat will result in increased risk for heat related illness. Little relief will be found during the night in the St Louis region as low temperatures will be from 75 to 80 in the City of St Louis and around 70 in outlying areas.
If anyone is overcome by heat, they should be moved immediately to a cool and shaded location. Heat stroke is an emergency; call 9-1-1 immediately.
Find additional information on this advisory from this interactive map, or by viewing the National Weather Service alert.