By Brad Brooks and Brendan O'Brien
(Reuters) -Powerful tornadoes and large hail may batter a large swath of the southern United States on Tuesday as forecasters warned millions of Americans to be prepared for dangerous weather throughout the day and into the evening.
Some 15 million people living in U.S. South and parts of Missouri, Tennessee and Kentucky were under the threat of severe weather that could produce powerful "long-track" tornadoes - twisters that stay on the ground far longer than normal tornadoes, the National Weather Service (NWS) said.
The NWS urged people to stay "weather aware" throughout Tuesday and into Wednesday as some thunderstorms could pack damaging winds of 80 miles per hour (128 km per hour) and tennis ball-sized hail while possibly spawning tornadoes.
By early afternoon local time on Tuesday, the NWS had issued a flurry of tornado warnings for the region. There were reports of high winds and small hail in some portions of Mississippi. Officials in Louisiana said that state government offices in eight parishes, or counties, were closed at noon so workers could head home before the storms.
The Mississippi Emergency Management Agency said on Twitter that the state's 3 million residents should prepare for power outages, stay off the roads and know a safe place to go in their home in case of a tornado.
The severe storms are being triggered by the collision of a cold front barreling down from the Rocky Mountains and pushing across the central plains, with warmer, moist air pushing north from the Gulf of Mexico, said Andrew Orrison, an NWS meteorologist based in College Park, Maryland.
He said the system could produce tornadoes with wind gusts of 111 mph and a slight chance for the most powerful twisters - with winds exceeding 200 mph - hitting the area.
Although tornado season runs from spring and into summer in the Midwest, the South has a secondary tornado season that occurs in November and December. In December 2021, a swarm of tornadoes tore through the Midwest and South, killing more than 80 people.