Thermal modeling is a powerful tool to infer the temperature regime of the ground in permafrost areas. We present a transient permafrost model, CryoGrid 2, that calculates ground temperatures according to conductive heat transfer in the soil and in the snow pack. CryoGrid 2 is forced by operational air temperature and snow depth products for potential permafrost areas in Southern Norway for the period 1958 to 2009 at 1 km spatial resolution. In total, an area of about 80 000 km<sup>2</sup> is covered. The model results are validated against borehole temperatures, permafrost probability maps from "Bottom Temperature of Snow" measurements and inventories of landforms indicative of permafrost occurrence. The validation demonstrates that CryoGrid 2 can reproduce the observed lower permafrost limit to within 100 m at all validation sites, while the agreement between simulated and measured borehole temperatures is within 1 K for most sites. The number of grid cells with simulated permafrost does not change significantly between the 1960s the 1990s. In the 2000s, a significant reduction of about 40% of the area with average 2 m ground temperatures below 0 °C is found which mostly corresponds to degrading permafrost with still negative temperatures in deeper ground layers. The thermal conductivity of the snow is the largest source of uncertainty in CryoGrid 2 strongly affecting the simulated permafrost area. Finally, the prospects of employing CryoGrid 2 for an operational soil temperature product for Norway are discussed.