In meteorology, we deal with average temperatures and average precipitation every day.
People want to know how our current conditions compare to the average.
But, these averages aren’t developed overnight.
The ideal method for determining averages takes many, many years of statistics.
The preferred period of time is at least 30 years.
This long time span tends to ‘smooth out’ the peaks and valleys of year-to-year temperature and precipitation variations.
So, when you hear about the average temperature or precipitation, you’re dealing with at least 30 years of information.