Thunderstorms pounded the Plains states and lower Mississippi Valley Saturday, bringing the threat of tornadoes and flooding. The storms were part of a system that began moving through Friday, producing tennis-ball-size hail and 80 mph winds in Texas, stretching through parts of Oklahoma and into Nebraska and Kansas.

The system was expected to push east Sunday and Monday, with the risk of large hail, damaging winds and tornadoes possible, the National Weather Service predicted.

The Houston Chronicle reported 40 homes flooded in La Porte, Texas, and emergency services officials said they received at least 17 calls from people stranded in cars. As much as 5.32 inches of rain was registered on rain gauges near the Houston Texans' football stadium.

The Associated Press reported an unconfirmed report of a tornado about 110 miles northwest of San Antonio but no damage or injuries were reported. noted large parts of the Plains received huge rainfalls earlier this week, raising the possibility of flash flooding throughout the area, with the gulf coast states under the greatest threat. "Even some locations farther north that don't see any thunder at all will still have heavy, steady rain to contend with," Meteorologist Evan Duffey said.

Heavy weather was forecast for Missouri, Illinois, Arkansas, Kentucky, Tennessee and Mississippi Sunday, taking with it the warmer temperatures of recent days and bringing the possibility of snow in some areas, especially as the system makes its way to New England. "The pattern will deliver several days of cooler-than-normal air and unsettled weather from the Midwest to the East Coast to end the month," long range expert Paul Pastelok said.

Eight tornadoes were reported Friday in northeastern Colorado, western Kansas and near coastal Texas, the Weather Channel reported. Damage was reported to fences and houses.