A government source that records rainfall by zip code is Climate Data Online. Climate Data Online provides free access to the weather records archived by the National Climate Data Center.
Climate Data Online provides access to global weather and climate information including daily, monthly, seasonal and yearly rainfall records. The search tool provides a data set that measures precipitatio every 15 minutes and every hour. A date range can also be selected. Once this information has been chosen, a map with the chosen zip code highlights the area and indicate how much rainfall coverage occurred in that area with a percentage amount.