Wildfires can significantly alter stream temperature in forested mountain catchments, with important consequences for aquatic ecosystems. As climate change drives more frequent and severe fires in the western U.S., understanding how streams respond is increasingly critical. In this study, we examined six small headwater streams in Oregon’s H.J. Andrews Experimental Forest before, during, and after the 2023 Lookout Fire. Using 75 sensors, we tracked daily temperature patterns and compared burned and unburned catchments. We found that stream temperature increased by 0.5–3°C in burned areas, especially where subsurface water storage was low. These low-storage catchments also saw larger daily temperature swings. In contrast, catchments with higher storage showed more stable temperatures, suggesting that groundwater inputs help buffer against post-fire warming. Our spatial models showed that the extent of warming was closely tied to both fire severity and catchment storage characteristics. These findings provide insight into which streams may be most vulnerable to fire-induced warming, and highlight the importance of subsurface water storage in maintaining stream resilience under a changing climate.