Precipitation is defined as "rain plus melted snow." In most cases, daily values are reported (some sites report hourly or even more frequently).
Mean Total Precipitation:
The mean monthly values were computed by taking the 30-year mean of the monthly means. The monthly means were computed from the sum of the daily precipitation values for a given month. The mean annual value was computed by taking the 30-year mean of the yearly means. The yearly means were computed by averaging their 12 monthly mean values.
Mean Number of Days with Measurable Precipitation:
The monthly values were computed by taking the 30-year mean of the number of days with measurable precipitation (at least 0.01 inch) for a given month. The mean annual value was computed by taking the 30-year mean of the yearly means. The yearly means were computed by averaging their 12 monthly mean number of days with measurable precipitation.