There is a severe risk of road icing and slipperiness when rain or sleet falls on a frozen road surface. Traffic can be severely affected, with a higher frequency of road accidents. These conditions usually occur during warm frontal passages when cold weather and low road surface temperatures are replaced by warmer air and precipitation. Two case studies from southern Sweden show the spatial and temporal distribution of rain or sleet on a frozen road surface. The influence of regional-scale characteristics is demonstrated. Air temperature governs the spatial distribution when temperatures around -10 °C precede the event. Weather stations in an open environment experience slippery conditions first. If temperatures are just below zero before the front arrives, road surface temperature becomes the crucial factor. Weather stations in locations screened by forest or road cuts are the first to register this event. The methodology presented in this paper can be used to increase knowledge of the spatial and temporal patterns of road slipperiness in an area. As a result, forecasts and maintenance activities can be improved and there is a better understanding of the relationship between synoptic events and road slipperiness.