United States

By Samantha Kramer, AccuWeather.com Staff Writer

July 08, 2012; 6:15 AM

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The summer's heat acts like a gas station for thunderstorms, said AccuWeather Severe Weather Expert Henry Margusity. (Photo courtesy of Photos.com)

Although many people see summer as the season to relax in perfect weather, a turbulent June proved that warm months are still prone to severe weather.

Hot and humid weather slammed the United States with four tropical storms, a derecho and intense heat waves already, all before the beginning of July.

Storms are usually carried by a jet stream in fall and winter months. Jet streams are channels of fast winds near the altitude where planes fly. While the jet stream weakens in the summer, a new source of energy is introduced into the atmosphere: heat.

The peak of tornado season ends in May. By late June and early July, tornado activity usually decreases by 50 percent, but that doesn't mean severe weather stops for the summer. Heat fuels an increase in the amount of thunderstorms and flooding threats.

"This summer's heat acts as a fuel for thunderstorms," said AccuWeather Severe Weather Expert Henry Margusity."You don't need the jet stream in the summer. It's like gas station season for thunderstorms."

A super derecho leaving a 700-mile trail of destruction across the Midwest and mid-Atlantic on June 29 demonstrated the ferocity of thunderstorms fueled by intense heat.

Despite tornado season dwindling, June was the most active severe weather month in 2012 with an estimated 3,700 damage reports from the Storm Prediction Center. May, even though it's usually the peak of tornado season, gathered 3,320 reports.

High tropical activity didn't make June any easier.

Tropical activity built up as the country came out of another La Niña winter, when sea surface temperatures are cooler than normal. According to the NOAA, the chances for the U.S. to experience hurricane activity during a La Niña season are substantially higher, which explains June's record-breaking number of tropical storms.

However, the intensity of tropical activity is expected to decrease as we trend into an El Niño phase, said AccuWeather Long-Range Forecaster Jack Boston.

El Niño is La Niña's counterpart and creates warmer-than-normal sea surface temperatures. El Niño pulls the jet stream farther south across North America, which sends a blast of high-level winds into the Atlantic ocean. The wind shear blows apart tropical storms in the ocean and limits hurricane activity.

Unfortunately, this doesn't mean it will be a calmer August.

Boston said to expect more severe thunderstorms throughout the summer as a result of the heat.

"As hot, humid air in the South runs into a jet stream from the Great Lakes, it will make a good setup for strong thunderstorms across the Northeast," Boston said.

Without the wind to move these storms quickly, Boston said the East can expect to deal with flooding issues.

"There won't be wind and hail, but the thunderstorms will move very slowly, which means more drenching rains," he said.