Pore pressure is important for the trigger of debris slides and flows. But how, exactly, does the pore pressure vary just before a slide happens? We drilled and installed a piezometer 1.6 m below the ground in a hillslope susceptible to debris flows in western Norway and measured pore pressure and water temperature through the years 2010–2013. We found the largest anomaly in our groundwater data during the storm named Hilde in November in 2013, when a debris flow happened in this slope.