Temperatures across much of the Midwest, including Chicago, remain well above normal. The 91-degree reading registered at O’Hare International Airport on Monday was the city’s hottest September 17th since 1955, when the day’s record high of 93 was established. Through the 17th, this month has run 5.8 degrees above normal. July-level warmth is to remain in place through Thursday, though a weak frontal boundary is expected to bring slight cooling on Wednesday. Scattered thunderstorms may also bring temporary relief from the sticky weather. Storms erupted along this front Monday afternoon, leaving trees and power lines strewn across portions of southeast Minnesota and central Wisconsin. Another surge of 90-degree heat is likely Thursday, before building high pressure north of lake Superior sends more substantial cooling into the area. Temperatures are expected to average closer to normal over the weekend.