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 every athlete’s training geared toward making and then peaking at 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 rain on Saturday, which could lead to athletes deciding to pull out rather than risk an injury that would keep them out of a trip to Rio.