Slow-moving remnants of Barry delivered 16 inches of rain in southwestern Arkansas on Tuesday, breaking the state's record for the most precipitation from a tropical system.
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What's left of Barry now is forecast to combine with a frontal system, producing more severe storms, rainfall and potential flooding.
Flash flood alerts were issued Wednesday morning in seven states from Minnesota to New Jersey. Some areas could see more than 4 inches.
The frontal system and tropical moisture from Barry also could ignite multiple severe storms in the Plains, the Upper Midwest and the Northeast later in the day.
Damaging winds, large hail and a slight chance for tornadoes are the biggest threats.
From Nebraska to New Jersey, two dozen states are under heat alerts on Wednesday morning, with the heat index in some sections probably topping 110.
The massive heat wave should continue into the weekend, from Kansas City to Chicago and all the way into New York City.