Flooding, storms, heat and humidity create dangerous weather mix in metro-east

The metro-east is headed for a potentially dangerous mix of weather events this week, including high heat indices, flash flooding and potential severe weather.

The National Weather Service released a heat advisory at midday Monday through Tuesday night. It predicts heat index values as high as 108 degrees in the St. Louis region early this week, including Madison, St. Clair and Monroe counties.

But Jared Maples, a forecaster for the National Weather Service in St. Louis, said scattered thunderstorms Tuesday could bring relief from the heat for some areas.

“If somebody gets under one of those, there will be some localized cooling,” Maples said. “But by and large, it does look like we’re headed into that heat.”

Relief is tempered by the risk of flash flooding as storms continue this week.

The National Weather Service issued a flash flood warning for Madison County Monday morning after the region received 2 to 4 inches of rain in a three-hour stretch. The warning includes areas of Roxana and Prairietown, but Maples said he’s also keeping an eye on Alton, Wood River, Granite City and Bethalto.

The entire metro-east remains under a flood watch through Tuesday morning.

The region is also at risk for severe weather Thursday afternoon into the evening.

Maples said high temperatures would cluster near metro areas and dense suburbs, where concrete and other development store heat and create a “heat island” effect.

The dew point is also expected to climb well above 70 degrees Tuesday and Wednesday.

Dew point is the lowest temperature at which the air can hold all of its moisture as water vapor. When the temperature dips below the dew point, water comes out of the air in liquid form as dew or fog.

The National Weather Service rates any dew point over 65 degrees as having an “oppressive” amount of moisture in the air.

With the dew point reaching upward of 70 degrees this week, Maple said the humidity and heat could create dangerous conditions.

“It just makes it really hard for sweat to evaporate,” Maples said. “The moisture that’s on your skin doesn’t evaporate as efficiently, so that can’t carry the heat away from your skin.”

The combination of high temperatures and high dew point is associated with a higher risk of heatstroke, according to the Illinois Department of Public Health. Warning signs for heatstroke include red and dry skin, rapid pulse, headache, dizziness, nausea and confusion.

The National Weather Service heat advisory recommends drinking plenty of fluids, wearing loose-fitting clothing and staying in air-conditioned rooms.

The city of Belleville will activate several cooling centers when the heat index reaches 105 degrees:

• Belleville Public Library, Main Branch: 121 E. Washington St., 9 a.m. to 8 p.m. Monday thru Friday and 9 a.m. to 5 p.m. Saturday and Sunday (618-234-0441)
• Belleville Public Library, West Branch: 3414 W. Main St., 9 a.m. to 5 p.m. Monday, Wednesday, Friday and Saturday and noon to 8 p.m. Tuesday and Thursday (618-233-4366)
• Programs & Services for Older Persons: 201 N. Church St., Monday thru Friday 8 a.m. to 4 p.m. (618-234-4410)
• The Salvation Army St. Clair County: 20 Glory Place, Monday thru Thursday 9 a.m. to 3 p.m. and Friday 9 a.m. to 1 p.m. (618-235-7378)