DES MOINES, Iowa (AP) The biggest unknown for the annual Drake Relays has always been the weather.
Conditions could be a big factor this year, especially with many athletes training for the Rio Olympics.
Drake has lined up stars like LaShawn Merritt, Kirani James, Jenny Simpson and Brittney Reese to compete in this year's meet, which starts in earnest Thursday and runs through Saturday. But the forecast calls for cool weather and rain on Saturday, which could force athletes to pull out rather than risk an injury that would keep them out the Summer Games.
Still, purses of up to $20,000 for the winners of the elite races could convince some top runners that the conditions can be overcome. Some of the story lines to follow for the 107th annual Drake Relays:
MEN'S 400: Six of the top 10 400-meter athletes in the world according to 2015 rankings are scheduled to run,- including the last two Olympic champions. Merritt, the 2008 gold medalist in Beijing, won silver at last year's world championships and is hoping for another trip to the Olympics. James, who took first at the London Games in 2012, set the Drake record at 44.23 seconds and finished just behind Merritt at worlds in 2015. Luguelin Santos of the Dominican Republic was fourth at the most recent world championships and will looking to show his early speed to James, who nudged him out for the gold medal in London.
NO HURDLES HERE: Aries Merritt, the gold medalist in the 110-meter hurdles in London four years ago, will be hoping to build off a third-place finish at the world championships in 2015. Hansle Parchment, David Oliver and Aleec Harris figure to be Merritt's main competition - but youngster Omar McLeod of Arkansas recently won an indoor world title at 60 meters. Neither Lolo Jones nor Dawn Harper-Nelson is scheduled to compete in the women's 100 hurdles. But a host of Rio medal contenders - including up-and-coming Jasmin Stowers, who finished 2015 ranked No. 3 in the world - are set for Saturday's race.
1,500 METERS: Simpson of the U.S. will begin her quest for a third straight Olympic berth at Drake. Mary Cain, who had the look of a future star in distance running before a disappointing season at Oregon, has moved back to her hometown of Bronxville, New York, in an attempt to capture the form that saw her capture a world junior title at 3,000 meters in 2014. The middle distance community will be watching Cain's time carefully because she has the raw ability to make an Olympic team at just 19.
BRITTNEY'S WORLD: Reese, a fan favorite for her ebullient personality, returns to Drake after recently winning the U.S. indoor title with a jump of 22 feet, 7.25 inches. Reese has won five world championships and claimed gold in London in 2012 - and a strong performance at Drake could let the rest of the world know she's a serious contender in Rio.
OTHERS TO WATCH: American Boris Berian won the most recent world indoor championship at 800 meters ... American Will Claye, the 2012 Olympic silver medalist in the triple jump, headlines the field in that event ... Javier Culson and Jeffrey Gibson of the Bahamas are two of the world's best in the men's 400-meter hurdles.