Some of the information provided, from such a source as NOAA, is represented as an average weather occurrence for a particular time period. Examples of this may be an average of 0.05 inches of rain on a specific date or an average of 10 inches of rain for a specific month, all of which is based on 30 years of data. However, converting directly from 30 year averages to a specific number of âreasonably anticipatedâ weather days is virtually impossible and is simply a guess.