Abstract Direct measurements of wildland fire plume properties are rare because of difficult access to regions near the fire front and plume. Moisture released from combustion, in addition to added heat, can enhance buoyancy and convection, influencing fire behavior. In this study, a mini unmanned aircraft system (miniUAS) was used to obtain in situ measurements of temperature and relative humidity during a prescribed fire. The miniUAS was successfully maneuvered through the plume and its associated turbulence and provided observations of temperature and humidity profiles from near the centerline of the plume. Within the plume, the water vapor mixing ratio increased by 0.5–3.5 g kg−1 above ambient and was caused by the combustion of fuels. Potential temperature perturbations were on the order of 2–5 K. These results indicate that significant moisture and temperature enhancement can occur and may potentially modify convection dynamics of fire plumes.