(CNN) - Nearly 50 million people are under threat of hail, heavy rain, strong winds and isolated tornadoes this week as several storms move east, according to the National Weather Center.
Storms spread across the Great Lakes/Ohio Valley area and most of the Northeast on Sunday. While the risk for severe storms appears to be low, it extends over a large population.
A severe thunderstorm watch is in effect until 10 p.m. Sunday for parts of New York, Pennsylvania and Vermont. A separate line of thunderstorms from the same system drenched northern Indiana and southern Michigan. In all, roughly 18 million people are affected.
In the central plains, nearly six million people are under a flash flood watch.
At least 38 tornadoes have been reported since Friday morning, including in Kansas, Nebraska and Texas. Saturday brought another 11 tornadoes along with 150 wind reports and 33 hail reports.
In Comanche County, Oklahoma, a tornado destroyed two homes Saturday morning, said Ashleigh Hensch, an emergency management spokesperson there. Another in Abilene, Texas, caused "widespread damage," CNN affiliated KTXS reported.
A tornado overturned a semi-truck on a Mineola, Kansas, highway with a driver inside, according to CNN affiliate WJTV.
This is peak tornado season, CNN meteorologist Derek Van Dam said, "with an average of 268 tornadoes countrywide during the month of May."
Threat of flooding will be high throughout the week, with rainfall totals ranging from one to five inches, according to Van Dam.
"The heavy rain will impact areas that have received significant amounts of rain within the past several weeks," Van Dam said. "The ground remains very saturated and may elevate the flood threat."
Missouri is expected to see heavy rain in recently saturated soils and may have increased flood potential, according to the NWS.
The Mississippi River has been above flood stage for 133 straight days at Natchez, 90 days and Vicksburg and 89 at Greenville, said the NWS, breaking record for some of the longest-lasting floods in years.
In early May, the Mississippi broke its July 9, 1993, record after heavy rainfall triggered flooding from Minnesota to the Gulf of Mexico, CNN affiliate WQAD reported. The flood gauge in 1993 at Rock Island, Illinois, topped out at 22.63 feet. Its level this month reached 22.64 feet, WQAD said.
Greatest threat to come later this week
Monday will see the greatest risk for severe weather, Van Dam said, as a cold front moves from the West into the Plains.
The Panhandle of Texas and Central Oklahoma will see a moderate risk of severe weather (level four out of five), with the threat of strong, violent tornadoes, very large hail and damaging winds, according to the National Weather Service Storm Prediction Center.
CNN's Robert Shackelford, Derek Van Dam and Theresa Waldrop contributed to this report.
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