We assess the major aspects of the subsurface thermal regime within crystalline rocks of southern Norway. Results of two-dimensional modeling of coupled groundwater flow and heat transfer demonstrate that advective cooling due to groundwater flow is an important factor for the reduction of subsurface temperatures in southwestern Norway (the Bergen and Stavanger areas) where the normal annual precipitation is high on the western (windward) side of the Scandes mountains. On the other hand, the influence of groundwater flow on subsurface temperatures is most likely relatively low in southeastern Norway (the Moss area), which represents the rain-shadow area with light precipitation and is characterized by smoothed landforms. Therefore, where the reduced subsurface temperatures are associated with high atmospheric precipitation and complex surrounding topography, deep groundwater flow is most likely present within crystalline rocks. In this case, the observed low values of the thermal gradient within crystalline rocks can be used as groundwater flow tracers.