Streams that receive snowmelt contributions have been hypothesized to remain cooler and have more streamflow during critical periods in the summer. Headwater streams in the Pacific Northwest are anticipated to experience major declines of snowpack in the future. To evaluate the potential effects of reduced future snowpacks on summer stream temperatures and streamflow, we explored 20 years of hydro-climatic data from gaged watersheds and weather stations in the H.J. Andrews Experimental Forest, Oregon, USA. The distribution of large and small sites across a range of elevations (400–950 m) allowed us to further explore spring and summer temperature and hydrologic responses to snowpack. We found that years with low snowpack corresponded to higher stream temperatures primarily in spring and early summer, but not in late summer. Other hydrologic and climatic variables, including timing of precipitation, were stronger predictors for late summer stream temperatures and streamflow. We also noted that the strength and persistence of snowpack influences on stream temperature were greater in the larger watersheds. Our findings suggest that for Mediterranean climates in the Pacific Northwest, snowpack variability has a limited relationship to summer stream temperatures and late summer streamflow. Instead, late-summer stream conditions appeared to be most influenced by multiple factors, including precipitation after snowmelt has ceased. We hypothesize that the timing of new water into these watersheds may be a critical predictor for late summer stream dynamics and when streams reach baseflow, rather than the form of water (rain or snowmelt) or its temperature.