Every year, folks ask us … “How does The Old Farmer’s Almanac predict the weather?” As America’s oldest weather forecaster, we specialize in predicting long-range weather, using a unique, age-old formula that’s traditionally 80% accurate.

Some think our forecasts are derived from folklore. According to weather lore, a long, hard winter can be predicted by lots of acorns, tough apple skins, and thick corn husks, while a mild one can be predicted by lower bees nests and thin onion skins. Have you ever looked inside a persimmon seed? It may give you clues, too!

While we can neither confirm nor deny the reliability of this folklore, we do know that, centuries ago, folks observed such phenomena and noticed corresponding, repeating weather patterns … so at The Old Farmer’s Almanac, we allow that there just might be some truth to it! However, folklore does not figure into the creation of weather forecasts in our annual almanac.

We’ve Predicted the Weather Since George Washington Was President

Our weather forecast methodology stems from a secret formula that was devised by our founder, Robert B. Thomas, in 1792, when George Washington was president. And believe it or not, it has nothing to do acorns, apples, wooly bear caterpillars, or persimmons!

Thomas believed that weather on Earth was influenced by sunspots, which are magnetic storms on the surface of the Sun. Notes about his formula are locked in a black box in our offices in Dublin, New Hampshire.

Almanac Editor-in-Chief Jud Hale shares the legend of the black box.

3 Disciplines in Long-Range Predictions

Over the years, we have refined and enhanced that formula with state-of-the-art technology and modern scientific calculations. We employ three scientific disciplines to make our long-range predictions:

solar science, the study of sunspots and other solar activity;

climatology, the study of prevailing weather patterns; and

meteorology, the study of the atmosphere.

We predict weather trends and events by comparing solar patterns and historical weather conditions with current solar activity.

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 often very close to our traditional claim of 80 percent.

What is “Normal” Weather?

When you read the weather predictions in this Almanac (or listen to any TV or radio forecast), you may notice the terms “normal” or “average” used to compare current traditions.

Most of us may think of the weather last year or in recent history. However, averages are based on 30-year periods prepared by government meteorological agencies and updated every 10 years. The most recent tabulations span the period 1981 through 2010. Before that, the base period used by the National Climatic Data Center (NCDC)—based in Asheville, North Carolina—was 1971 through 2000. This involves sweeping up the period’s daily temperature, precipitation, and other weather information from more than 7,000 weather stations around the country and computing new statistics to be rolled out.

The Old Farmer’s Almanac forecasts “deviations from averages,” using the official 30-year normals for temperature and precipitation, averaging each of our designated regions. Technically, we use the normals rather than the averages. (Although the spline-curve modifications affect the daily normals, they have no discernable effect on the monthly normals that we use—so in this case, the normals and averages are actually the same.)

The 2021 Old Famer’s Almanac is Now Available!

Find 12 months of weather predictions and so much more! The 2021 Old Farmer’s Almanac is now available in bookstores and shops across America. Find local retailers at Almanac.com/Wheretobuy.

If you’re “stuck at home” or simply prefer to order your copy online to ship straight to your home, go to thealmanacstore.com.