Updated story

Following a day that tied the record for the city's hottest Fourth of July ever, summer classes at some 18 Chicago Public Schools schools were canceled and two died of heat-related causes in Cook County Thursday.

The summer classes were canceled at schools that lack air conditioning due to a weather forecast that includes temperatures as high as 105 both Thursday and Friday in Chicago, WLS reports. An excessive heat warning is in place across the Chicagoland area through Friday evening.

The Chicago Sun-Times has a full list of schools that canceled classes Thursday.

The weather has lead to the death of two people in Cook County as of late Thursday afternoon, the Chicago Tribune reports. Their deaths mark the first reported heat-related deaths in the county this summer.

A sudden downpour Thursday afternoon caused temperatures to temporarily fall several degrees in the Chicago area, but temperatures soon returned near the day's high O'Hare Airport reading of 103 degrees, a new record high for July 5.

That temperature falls only two degrees shy of the city's hottest day on record which, according to the Chicago Weather Center, was July 24, 1934, when the official temperature was recorded at 105 degrees.

The heat, as of Thursday morning, has led to the closure of a section of Columbus Drive in the city's South Loop, NBC Chicago reports. The street buckled near Roosevelt Road Wednesday afternoon, creating a large bump.

The heat also likely contributed to a power outage and evacuation at the Shedd Aquarium Thursday afternoon, CBS News reports. The outage never threatened any animals housed there because a generator kicked in immediately. The aquarium is expected to reopen Friday.

Thursday has been declared an Air Pollution Action Day, ABC Chicago reports.

If temperatures Friday follow in Wednesday and Thursday's footsteps and also crack 100, the city would see the first string of three consecutive 100-degree-plus days since 1947, the Chicago Tribune reports.

Friday's previous record high is 99, set in 1988.

Relief from the oppressive heat is not expected to arrive until Saturday afternoon, when clusters of thunderstorms and rain showers move into the area, meteorologist Tom Skilling forecasts.

Area residents without air conditioning are urged to go to a cooling center -- such as a public library or police station -- to help them beat the heat.

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