A possible synoptic source of water for alluvial fan formation in southern Margaritifer Terra, Mars

► Alluvial fans in Margaitifer Terra likely formed by synoptic precipitation. ► Snow was possibly concentrated into crater rim depressions by the wind. ► Snow facilitated physical weathering and provided runoff to fans upon melting. ► Fans may record and preserve evidence of habitable conditions on Mars. ► Fan development is associated with late, ephemeral wet interval during a colder, otherwise drier period on Mars.