Turnbull came down to the Hawkeyes from White Bear Lake, MN. He made 15 appearances as a Freshman, starting four of them and earning his first win in his Hawkeye debut. His Sophomore season, in 13 starts Turnbull led the team in strikeouts with 44. He followed that up the following season with only 7 starts and his strikeout total dipped to 31 while going 3-5. His Senior season, his record dropped to 1-3 while he finished up with a 5.29 ERA. Turnbull went on to be selected in the 17th Round of the Amateur Draft by the Toronto Blue Jays. His first season was spent with the Auburn Doubledays of the New York-Pennsylvania League. In 2010, he moved up to the Class A Lansing Lugnuts where he compiled 21 saves while going 3-3 with a 3.86 ERA in relief. He started 2011 with the Lugnuts as well, garnering an All-Star selection in the Midwest League, but finished the season on the roster of the Dunedin Blue Jays in the Class A Advanced Florida State League.