In early April, the Kansas atmosphere can yield anything from a perfect storm to a perfect day.

Sunday hit the optimum for the field of 1,500-plus runners who participated in the Raintree Run half-marathon, 5K and mile fun walk.

“It might have been a little cool early,” said Steve Riley, who manages the event with wife Marcia, “but it doesn’t get better than this.”

When the runners left Raintree Montessori School at 8 a.m., the temperature was around 40 degrees, but the wind was light, and the sun was shining.

By the time the 5K runners came in about a half an hour later, many had shed their warm tops. And when the half-marathoners started coming in about 9:15 a.m., the thermometer had climbed at least another 10 degrees.

“It was perfect weather for the half-marathon,” Riley said, “and the times showed it. They were real good.”

Take Michelle Hein.

Hein, who lives and works in Topeka, won the women’s division of the Raintree Run half-marathon in 1:27:31 two years ago. She finished second last year with a clocking of 1:27:53.

“If I ran 1:25 or under this year I would have been happy,” said Hein, a 28-year-old former Emporia State runner who grew up in Hays.

Minutes later, she learned her official clocking was 1:22:05.

“That’s my fastest half-marathon by three minutes,” the 5-foot-2 Hein said. “Last year was a little more windy than this, and I have some problems with the wind because of my size.”

Half-marathons aren’t that common in Kansas. At this time of year, they’re usually tune-ups for marathons later in the year.

“My focus right now,” Hein said, “is the Chicago Marathon, and I’m just trying to get in some races.”

In the men’s half-marathon, Vincent Topiwo, a native of Kenya who lives in Lenexa, ran 1:09:35, and was 24 seconds shy of the event record.

In the 5k, the overall male and female winners were Eric Graham of Olathe and Megan Manthe of Kansas City, Kan. Graham was clocked at 16:06, Manthe at 18:37.

Sunday’s weather helped lure the largest group of participants in the 10 years of the Raintree Run, a fund-raiser for the Montessori school.

“We’re over 1,500 for the first time,” Riley said. “I’m not sure of the exact number, but it just keeps getting bigger.”

How big can it become?

“We could handle more people,” he said. “The problem would be the (South Lawrence Trafficway) bike path. We could get bigger, but 2,000 would be pushing it.”

The Raintree Run is one of the largest running events in Kansas. Proceeds go for scholarships and to make improvements on the Montessori campus in southwest Lawrence.

In the past, the Raintree Run has helped the school purchase playground equipment, plant trees lost in a tornado and construct a mile-long running path, making the activities on the campus accessible to all children.