The hottest year on record in Utah remains 1934, a black-swan year if ever there was one.
However, we are making a run at it this year. For the year-to-date through the end of October, 1934 and 2015 are in a near dead heat with statewide average temperatures of 54.8ºF and 54.9ºF, respectively.
November and December 1934 brought temperatures that were 2.6ºF above average, so that's the number for November and December 2015 to aim for. Lots can happen in November and December, so I'm not making any predictions. I do suspect that unless we get really cold in December, something in the top 5 is virtually assured.