A significant heat wave that has broiled much of the Midwest this week is spreading farther east on Wednesday, bringing the potential for record-breaking high temperatures to millions more people. Little relief is expected for much of the country until the weekend.<\/p>\n
More than 160 million people are under extreme heat warnings or heat advisories, and for many it was the second or third straight day of severe warnings to avoid being outside in the warmest parts of the day.<\/p>\n
Triple-digit temperatures are being made worse by high levels of humidity, leading to oppressive heat index<\/a> readings. Many emergency officials and meteorologists say the heat index is a more accurate measure of what if feels like outside than temperature alone.<\/p>\n And on Tuesday, the heat index was brutal: 106 in Chicago<\/a> on Tuesday; 113 just north of Milwaukee<\/a>; 103 in Cleveland<\/a>; 113 in Southern Illinois<\/a>. On Wednesday, the Weather Service said, cities from Kansas City to Boston will likely record heat index values between 100 and 115 degrees.<\/p>\n Radley Horton, a professor at Columbia University\u2019s Climate School, said this particular heat wave has been characterized by especially high humidity.<\/p>\n \u201cAnd when the amount of moisture in the air is particularly high, it tends to make nights that much warmer,\u201d Dr. Horton said. \u201cTemperatures don\u2019t change as much between daytime and nighttime.\u201d<\/p>\n Key things to know about the heat wave todayThe day-by-day forecastWednesday<\/p>\n Most of the East Coast will be at some risk of dangerous temperatures, according to the Weather Service, but the most extreme temperatures will remain in the states around the Great Lakes.<\/p>\n Most of Wisconsin, Ohio, Michigan and Illinois will be under the service\u2019s most extreme and rare warning level, reserved for long-lasting heat that offers little to no relief at night.<\/p>\n Bob Oravec, a meteorologist at the Weather Prediction Center, said Wednesday was expected to be \u201cthe first big hot day,\u201d with areas of Michigan, Ohio, Pennsylvania and New York expected to see the most anomalous temperatures on Wednesday.<\/p>\n \u201cThat\u2019s because typically their average temperature is lower,\u201d he said. \u201cBut the highest temperatures on Wednesday are really not going to be much different anywhere. From the Great Lakes to the Ohio Valley to the Northeast, they\u2019re going to reach 95 to 100.\u201d<\/p>\n Washington, D.C., could reach 100 degrees for four consecutive days between Wednesday and Saturday \u2014 with the potential to tie a record for the city, said Michael Muccilli, a meteorologist with the National Weather Service.<\/p>\n