Some hibernating bats in thermally stable, subterranean roosts have experienced precipitous declines from white-nose syndrome (WNS). However, some WNS-affected species also use thermally unstable roosts during winter which may impact their torpor patterns and WNS susceptibility. From November to March 2017-2019, we used temperature-sensitive transmitters to document winter torpor patterns of tri-colored bats (Perimyotis subflavus) using thermally unstable roosts in the upper Coastal Plain of South Carolina. Daily mean roost temperature fluctuation was 4.8 ± 2°C SD in bridges and 4.0 ± 1.9°C in accessible cavities with maximum fluctuations of 13.8°C and 10.5°C, respectively. Mean torpor bout duration was 2.7 ± 2.8 days and was negatively related to ambient temperature and positively related to precipitation. Bats maintained non-random arousal patterns focused near dusk and were active on 33.6% of tracked days. Fifty-one percent of arousals contained passive rewarming. Normothermic bout duration, general activity, and activity away from the roost were positively related to ambient temperature, and activity away from the roost was negatively related to barometric pressure. Our results suggest ambient weather conditions influence winter torpor patterns of tri-colored bats using thermally unstable roosts. Short torpor bout durations and potential nighttime foraging during winter by tri-colored bats in thermally unstable roosts contrasts with behaviors of tri-colored bats in thermally stable roosts. Therefore, tri-colored bat using thermally unstable roosts may be less susceptible to WNS. These results highlight the importance of understanding the effect of roost thermal stability on winter torpor patterns and the physiological flexibility of broadly distributed hibernating species.