Thousands of runners took to Fort Worth's streets for the Cowtown Half Marathon Sunday morning.

After hours of steady snowfall across North Texas, Cowtown Marathon officials canceled several race activities this weekend.

The Half Marathon began 8:00 a.m. Sunday morning. All Sunday registered runners were invited to join the half marathon. No bib or registration changes were required.

"Participant safety is priority one and conditions don't appear favorable for today and Saturday morning," said Heidi Swartz, Cowtown Executive Director. "We've spoken with city officials and the National Weather Service (NOAA) and feel confident that Sunday's events can proceed."

Participants were told to use extreme caution in traveling to Will Rogers Memorial Center on Sunday. the Harley Street and Farrington Field parking lots are currently ice-covered, and may not be completely cleared by Sunday morning.

The full and ultra-marathon courses take in a considerable amount of secondary streets in shaded neighborhoods, including the Trinity Trail. Officials said these stretches of the course will not be passable for runners by Sunday race time.

Your Snow Photos - February 26, 2015

Swartz said the race would be open Saturday from 1 p.m. to 6 p.m. for runners to check-in for Sunday's delayed race and pick up packets. Runners can still register for Sunday's races on Saturday at the Expo.

"We encourage participants to carefully make their way to the expo on Saturday afternoon to shop and pick-up their packets," said Swartz. "Please come to the expo with your bib number and be patient as our volunteers assist you. Don't wait until Sunday morning, since we won't be able to accommodate everyone at packet pick-up just before start time."

Thousands of runners, like Shawna Robinette spent Thursday and Friday watching the forecast.

"Snow I can handle, rain I can handle, wind I don't like it but I can deal with it," Robinette said. "Ice is a deal breaker."

Robinette is one of the 28,000 people who signed up for the 37th annual Cowtown Marathon. This year marks a new record for sign-ups.

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In the 37-year history of the Cowtown they've certainly seen rain, but only dealt with ice once.

"The first year the Cowtown happened in 1979 there was an ice storm the night before the race and it took place," Swartz said. "There were only 600 runners that year. So, it was easier to take place with 600 runners versus 28,000 or 30,000."

Events originally scheduled for Saturday, including the 10K, 5K and Cook Children's 5K, will not be rescheduled.

Playing in the Snow - February 27, 2015

"We are so grateful to the thousands of runners, volunteers, supporters and city employees who regularly participate in our event. Their dedication, patience and flexibility in times like these are invaluable," said Swartz.

Cowtown organizers tweeted Friday night that runners would be able to complete Saturday's races virtually.

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Here is the revised schedule:

Saturday, Feb. 28

Expo Open: 1:00PM-6:00PM (Packet pick-up for all races, shopping)

Sunday, March 1st