A wall of moisture flowing north from the Gulf of America wasbringing weather havocand the threat of tornadoes to a broad stretch of the South on Sunday and was forecast to continue dumping heavy rains through Memorial Day. The ominous weather comes as a record-breaking number of Americanswere predicted to travelover the holiday weekend. But Sunday's Indianapolis 500 should be run without weather interuption, forecasters say. A massive and somewhat stationary front extending from the Southeast to the Southern Plains and Central Rockies was expected to remain in place through Tuesday, the National Weather Service said. "Numerous" flash flooding events are possible and many streams could flood, affecting larger rivers, for parts of the Southern Plains and Lower Mississippi and Tennessee Valleys, the weather service said. "The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail and a few tornadoes," forecaster Paul Ziegenfelder wrote May 25 in a public discussion on the Weather Prediction Center website. "There is an increased risk of severe thunderstorm wind gusts of 75 mph or greater and hail, two inches or greater, over the Southern Plains." Storms, rainfall:Unsettled weekend in parts of US Flood watches were posted Sunday over parts of Texas, Oklahoma, Arkansas, Missouri and Kansas. Major cities that could be most affected by weather Sunday included Oklahoma City, Little Rock and Memphis. The weather service office in Memphis warned that parts of the area on Sunday could see 60-mph wind gusts and hail the size of quarters. The forecast was enough for Memphis officials to postpone for one week the annual Lemon Drop Festival in Court Park. The Memphis Symphony Orchestra was hoping to go forward with its outdoor concert Sunday night. Showers and thunderstorms were forecast for Monday into Tuesday, threatening a host of outdoor Memorial Day events in the city. 45M Americans will be on roads:: How to avoid the worst Memorial Day traffic Last year's Indianapolis 500 weather included grandstand-clearing thunderstorms and a more than four-hour rain delay that bumped the end of the race perilously close to sundown. This year? "Scattered sprinkles after noon" are the biggest meteorological threat facing the 109thrunning of the "Greatest Spectacle in Racing." The weather service's Indianapolis office is predicting mostly cloudy skies with the possibility of light rain over the Speedway. The daytime high temperature is expected to reach 68 degrees, and winds are expected to remain mild. If that forecast holds, it looks like near-ideal weather for a clean and on-time race. −Eric Larsen,Indianapolis Star AAApredicted 45.1 million Americanswill travel domestically for the holiday weekend – an increase of 1.4 million from last year.Long holiday weekends are ideal for travelbecause so many people have an extra day off work and students have Monday off from school "Memorial Day weekend getaways don't have to be extravagant and costly," said Stacey Barber, vice president of AAA Travel. "While some travelers embark on dream vacations and fly hundreds of miles across the country, many families just pack up the car and drive to the beach or take a road trip to visit friends." AAA also predicts a surge of 2% in air passengers for the holiday weekend.Read more here. − Kathleen Wong This article originally appeared on USA TODAY:Tornadoes, storms, hail could disrupt Memorial Day travel, events
