Chicago weather: Heat advisory in effect across Illinois as heat index climbs, high temperatures hang on

July 18, 2013 (CHICAGO)

PHOTOS: Chicago beats the heat

A heat advisory is in effect for much of the state until 7 p.m. Friday. In Chicago, the worst of it is expected midday Thursday, with temperatures in the low-to-mid 90s, which means the heat indexes could reach 98 to 105 degrees, and on Friday, when some parts of the state could climb as high as 108-degrees on the heat index. Thursday's overnight low will only drop to the upper 70s.

That intensity, combined with the long duration of heat led the National Weather Service to issue the heat advisory. Severe weather may bring cooler temperatures in with it for the weekend.

The heat could cause rolling blackouts and buckle pavement, already Metra trains are running on heat delays of 10 to 15 minutes. Metra released a statement, "When temperatures exceed 95 degrees, it is necessary to operate our trains at reduced speeds to compensate for heat-related stresses on our track, switches and signals. During this heat event, we will have all resources on standby so we can quickly respond and restore service."

On Thursday morning, an underground transformer blew on the city's Northwest Side. ComEd crews worked overnight to get power back on. And part of U.S. 30 in Crest Hill was closed for several hours while IDOT crews worked to patch a hole.

Officials are urging residents to seek out shelter at cooling centers, drink lots of fluids, especially water, and check on neighbors. People should avoid being outside during the height of the heat, and exercise should be done during the early morning. Hot weather safety tips

At Brookfield Zoo, zookeepers are helping the animals keep cool with icy treats. Tim Sullivan, who has worked at Brookfield since he was a teenager, said while it's hot, the polar bears and other big animals aren't as uncomfortable as you might think.

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