Chicago area high temperatures reached the lower 80s Friday, marking the city’s 21st straight day that the mercury has reached at least 80, a string that began on July 28. More 80s are expected this weekend and probably on Monday, before ending Tuesday when cooler weather arrives in the wake of a cold front, likely holding highs in the middle and upper 70s. Scattered thunderstorms brought some much-needed rainfall to portions of the Chicago area late Thursday night and early Friday morning. Friday was dry across much of the Chicago area, though some late-afternoon thunderstorms developed along the lake breeze front bringing brief, heavy downpours to some inland locales. Great weather is expected for this weekend’s annual Chicago Air and Water show with sunny and warm weather conditions. The city’s next chance for rain should hold off until Monday when a cold front approaches the city.