U.S. weather experts say a major tornado outbreak and severe storms are set to hit the MidWest again on Wednesday afternoon and evening as a deadly storm season continues to threaten after weeks of destruction.

“Conditions are favorable for long-track, violent tornadoes in both the Moderate Risk and High Risk areas,” the National Weather Service said in an update Tuesday.

Tornadoes are expected to hit the mid-Mississippi and lower Ohio Valleys, according to NWS.

The NWS Storm Prediction center expanded the high risk area for severe thunderstorms to include parts of Arkansas, western Tennessee, southeastern Missouri, southern Illinois, western and central Kentucky and southern Indiana.

A moderate risk zone extends from southern Arkansas and Mississippi to central Indiana and western Ohio, SPC said.

As the risk of severe thunderstorms continues following tornadoes in the MidWest and South over the past few days, a new compilation of impact in 2011 finds that nearly 500 people have been killed and about 1,000 twisters have struck so far.

Tuesday saw destruction in Oklahoma, Arkansas, and Kansas, and on Sunday in Missouri.

At least 122 people died as a result of tornadoes in Joplin, Missouri on Sunday. In total, 487 people have died in 2011 due to Tornadoes, according a compilation by the Associated Press.

Meanwhile about 1,000 tornadoes have struck this year. The average has been 1,274.

It's the deadliest tornado season since 1953, when 519 people died.

On Tuesday evening, 15 deaths were reported, including 10 in Oklahoma, three in Arkansas and two in Kansas, authorities, said, according to CNN.

 Unfortunately, this event will likely continue for some time, said Oklahoma Gov. Mary Fallin on Tuesday. I am asking all Oklahomans to stay aware of the weather and to take proper precautions to keep themselves out of harm's way.

In Oklahoma, the tornado outbreak has prompted an emergency response at the local, state and federal levels.