Precipitation characteristics and their connection with atmospheric conditions are studied for the Greenland-Iceland-Norwegian (GIN) Seas during wintertime using satellite microwave (Special Sensor Microwave/Imager) and SSM/T2 data. A snowfall algorithm using SSM/T2 data is presented, which makes it possible to estimate the total precipitation and the relative contribution of each precipitation component (rain or snow) over open water. The monthly mean snowfall rate distribution compares well with the snowfall frequency derived from shipboard present weather reports although no data are available for direct snowfall rate validation. The retrieved results show that more than half of the precipitation falls as snow in the GIN Seas during winter and that the monthly mean horizontal distributions of rain and snow have different patterns. By examining the relationship between surface wind and precipitation and conducting case studies, it is found that rainfall and snowfall are associated with different weather types: rainfall occurs mainly in low pressure systems, while snowfall is more likely associated with cold air outbreaks.