The National Oceanic and Atmospheric Administration maintains a detailed record of historical data relating to climate and weather events. Rainfall totals are among the data sets which are publicly searchable and indexed over a customizable time period.
Historical records for precipitation are available dating as far back as 1895, though more recent rainfall totals appear in a more concise manner with the use of radar maps.
According to NOAA's records, the first five months of 2015 had the highest rainfall total for any prior year since the organization began keeping records. A total of 20.11 inches fell from the first day of the year until the end of May.
At the other end of the spectrum, 1996 had the driest 5-month start to the year, with just 4.34 inches from January to May.
NOAA also provides additional tools for tracking temperatures, extreme weather events and winter weather. Using these tools, a person can identify a wide array of details and begin spotting trends that are occurring in specific regions, such as an upward trend in temperatures during the summer months, or a downward trend in annual precipitation totals. Care must be taken to avoid leaping to conclusions, though, as these tools only provide a factual representation of history.