Milwaukee County and southern Wisconsin under an excessive heat warning again today

Milwaukee County is entering its second day of extreme heat, which has brought school closures and uncomfortable temperatures in the 90s.

Yesterday, Milwaukee recorded a peak temperature of 94 degrees, according to the State Climatology Office , with heat indices making things feel 100 degrees or warmer in some areas. This nearly broke the Aug. 26 daily temperature record of 96 degrees, and today is expected to be even hotter.

Milwaukee County, along with all of southern Wisconsin and northern Illinois, is under an excessive heat warning Tuesday from 11 a.m. to 7 p.m., the National Weather Service states . Early afternoon temperatures are expected to reach 88 degrees today in Milwaukee near Lake Michigan, with a heat index of around 99 degrees in the forecast between 11 a.m. and 3 p.m.

Things heat up as you move away from the lake ― south-central communities including Janesville, Lake Geneva, Watertown and Waukesha are expected to see heat indices between 105 and 107 degrees, NWS says .

NWS issues an excessive heat warning when the maximum heat index temperature is expected to be 105 degrees or higher for at least two days and nighttime air temperatures will not drop below 75 degrees.

Luckily, things are expected to cool down to near-normal across the state by Wednesday after a cold front comes through late Tuesday into Wednesday, local NWS meteorologist Benjamin Sheppard said. Daytime highs in the low 80s are expected in Milwaukee tomorrow.

"The winds behind that front in the middle of the day Wednesday are expected to ... turn northeast," Sheppard said. "So, the wind is essentially moving from Lake Michigan over Milwaukee, and that's going to make it feel a lot cooler and be a lot cooler."

More: Milwaukee County is under a heat advisory today. What does that mean?

Why is it so hot in Wisconsin today?

There is currently a pattern in the jetstream known as a "ridge," Sheppard explained. A ridge is an elongated area of relatively high atmospheric pressure that brings hot, humid weather.

The ridge is currently positioned directly over Wisconsin. "Essentially what that does is it allows for really warm, really humid air from the South to sit in place in our region, and allows the sun to cook those temperatures up to a really uncomfortable level," Sheppard said.

Will it storm in Milwaukee today?

Storms are possible in the Milwaukee area today, with chances increasing throughout the afternoon, NWS says. There is a chance of rain and thunder all day long, but it's most likely between 5 and 10 p.m., with precipitation peaking near 50% at 7 p.m.

"One or two broken lines of thunderstorms may pass through the region this afternoon (and) evening, with a threat for damaging wind gusts, frequent lightning and possibly hail," NWS shared in a social media post.

What does 'heat index' mean?

Heat index is a measurement of what the temperature feels like to the human body. It takes into account relative humidity combined with the air temperature.

• When the heat index is between 80 and 90 degrees, fatigue is possible the longer you're outside and/or with physical activity.
• When the heat index is between 90 and 103 degrees, there's a greater chance for heat stroke, heat cramps or heat exhaustion the longer you're outside and/or with physical activity.
• A heat index of 103 to 124 degrees enters the "danger zone," the National Weather Service says. Heat cramps or heat exhaustion is likely and heat stroke is possible the longer you're outside and/or with physical activity.
• A heat index of more than 125 degrees, rare in Wisconsin, is in the extreme danger category. Heat stroke is highly likely when you're exposed.

Hot weather safety tips

Hot weather can cause heat-related illness and even death. The Milwaukee Health Department and Centers for Disease Control and Prevention offer these hot weather safety tips:

• Slow down and limit physical activity.
• Spend time in air-conditioned spaces such as shopping malls, movie theaters or libraries.
• Don't leave kids or pets in a parked car. Temperatures can become life-threatening within minutes.
• Wear lightweight, loose-fitting and light-colored clothing.
• Take cool baths or showers. Use wet towels on your skin to cool down.
• Don't rely on fans as primary cooling devices.
• Drink plenty of water.
• Avoid consuming caffeinated or alcoholic beverages, which can increase heat effects.

Wisconsin weather warnings

Wisconsin weather radar

This article originally appeared on Milwaukee Journal Sentinel: Milwaukee County and southern Wisconsin under an excessive heat warning again today