Rain Stats. Filed in Posted on January 25, 2013 12:52 pm by Justin Shaw. Seattle averages 37.49 inches of precipitation a year, with the vast majority falling as rain instead of snow. Official precipitation totals for the city are measured at Sea-Tac Airport, which is actually located south of the Seattle city limits.eattle had never seen a daily rainfall of 4 inches or more until Oct. 20, 2003, when a torrential 5.02 inches deluged the city—setting a new record for the wettest day in Seattle history.