The heat have will tighten its grip on the Chicago area today, with temperatures in the middle 90s and a heat index as high as 106 in some places.
And it’s going to feel worse Thursday before we get a break late Friday as a cold front moves through and triggers thunderstorms. Cooler and less humid air will follow for the weekend, but the respite will be brief.
An air quality alert has been issued for northwest Indiana.
The heat index determines how hot it feels by factoring in both relative humidity and air temperature. A heat index reading of about 105 degrees or above is considered dangerous because it becomes more difficult for the body to cool itself. Cramps, heat exhaustion and heatstroke can develop.
The smothering weather is coming from a mammoth hot air mass — Summer 2013’s hottest to date — that’s draped across virtually the entire Lower 48, stretching nearly coast to coast.
This is an air mass with origins in the tropics. Thunderstorms that erupt in such weather don’t have the cooling power of storms that typically roam these parts. But the showers predicted over the next three days will, at least, help mix the air here, reducing prospects of serious air-quality issues.
Tuesday’s official reading of 92 was 2013’s hottest and Chicago’s highest temperature since last Aug. 31, nearly 11 months ago. Other area highs included 93 degrees at Midway and 91 at Chicago’s lakefront.
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