The Old Farmer’s Almanac has been offering weather predictions since 1792, but we wondered: What are the forecasts based on, and how accurate are they?

According to the publisher, the Old Farmer’s Almanac bases its forecasts on a “secret formula” derived by the almanac’s founder, Robert B. Thomas. “Thomas believed that weather on Earth was influenced by sunspots, which are magnetic storms on the surface of the Sun,” the book says. Over the years, the publishers refined that formula to include data from solar science, climatology, and meteorology. They predict weather trends based on historical weather conditions and current solar activity. They also use 30-year statistical averages from NOAA and other government agencies.

As for accuracy, the Almanac’s website says, “although neither we nor any other forecasters have as yet gained sufficient insight into the mysteries of the universe to predict the weather with total accuracy, our results are almost always very close to our traditional claim of 80 percent.”

This year, the Almanac has predicted higher than normal precipitation in much of Colorado. You can check the predictions for your area at the website: http://www.almanac.com/weather/longrange/CO