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The sky and weather conditons can change in a hurry in the weather pattern through Friday. (Angry clouds over Tamaqua, Pa., May 29, 2012, by AccuWeather.com Facebook fan Ryan F.)

This story has been updated and includes separate articles on the severe weather risk for the Midwest and South, as well as the East.

The risk of damaging thunderstorms will spread into the Midwest and South Thursday and then into part of the East Friday.

As the outbreak spreads eastward, it is likely to produce a swath of downed trees, power outages, large hail and isolated flash flooding. There is also the risk of a few tornadoes.

An unusually strong storm system for late May will continue to roll out of the Plains and toward the Great Lakes during the balance of the week.

Cold upper levels of the atmosphere will combine with strong surface heating to produce the rapid development of thunderstorms.

The storms will bring a raised risk for hail since the air is so chilly aloft. However, since the storms will poke high into the atmosphere, where strong winds are present, some of the strong, high-level winds can reach down to the surface in the form of powerful downdrafts and horizontal gusts.

The early stages of the severe weather took aim at the Plains late Thursday, as thunderstorms dropped hail as large as grapefruits and generated wind gusts as high as 90 mph. Meteorologist Bill Deger has more on those damaging storms

Later today and into tonight, more severe storms will target a large area from Texas to the Ohio Valley with damaging winds, hail and even a few tornadoes.

As it is now, an outbreak of large, long-tracking tornadoes is generally not expected east of the Mississippi, but rather more on the order of the straight-line wind and hail scenario.

Even with the setup as it is, brief tornadoes are still possible with the event in portions of the Ohio, Tennessee valleys as well as part of the central Appalachians and East Coast.

People should take the severe weather threat seriously and keep an eye on rapidly changing weather conditions.

The greatest threat to lives from any thunderstorms is lightning. Seek shelter indoors as storms approach. If you can hear thunder, you are at risk for being struck by lightning.

The storm system is more typical of early April in terms of the potential for severe weather.

According to Chief Meteorologist Elliot Abrams, "The pattern coming up in June will seem more like April, while May may have seemed more like June for some folks."

Abrams was referring to the relatively weak land-based storms in the Central and Eastern states, while the tropics were active in May.

The upcoming pattern well into June will tend to favor stronger land-based storms and the likelihood of minimal tropical activity due to wind shear.

AccuWeather.com Meteorologist Bill Deger contributed to the content of this story.