Danny Easum wipes his brow in front of a fan at Ace Brake and Steering, 541 Minnesota, on Wednesday, August 11, 2010.

Temperatures climbed above 100 degrees for the fourth straight day Wednesday, bringing little relief from this week’s brutal heat wave.

And the misery is only expected to continue, according to the National Weather Service, which has extended the excessive heat warning until 8 p.m. Friday.

Temperatures could reach 100 degrees, with heat indexes in the 115-degree range, through the remainder of the work week.

Blistering heat may be dangerous during the day, but what makes this heat wave especially hard to tolerate are high overnight humidity levels coupled with overnight temperatures that aren’t dropping as much as they had been, according to state climatologist Mary Knapp.

Knapp says although our high temperature peaks in the late afternoon, heat indices will be at their highest in the middle of the night. So if you’re expecting a break from the heat during overnight hours, it isn’t happening.

“People can tolerate higher temps during the day, but we’re not getting relief at night with temperatures and dew points staying high,” Knapp said.

This type of heat wave is particularly dangerous in an urban environment, where concrete and asphalt heat up the ground.

We may see lower temperatures next week, but that doesn’t necessarily mean it will feel cooler outside.

“The big question will be: Does that 89- or 90-degree day come with lower humidity,” Knapp said. “If the dew point is in the 76- to 79-degree range, the relief may not be as noticeable as we would like.”