Don’t say we didn’t warn you. The 2016 Old Farmer’s Almanac forecasts an unusually harsh winter this year for most of the nation.

The almanac, which is published annually and uses a secret forecasting formula it says is traditionally 80 percent accurate, has been in use since 1792 and remains one of the oldest and one of the most popular reference guides in the U.S.

The 2016 almanac, out today, warns the U.S. should prepare for extremely cold temperatures and lots of snow this winter. It says the Northeast can expect below-normal temperatures, the South will have above-average snowfall, and the Midwest will have less snowfall, but temperatures will be below-normal. The Pacific Northwest will see their biggest snowfall in mid-December, early to mid-January and mid to late February.

The secret forecasting formula, now locked in a black box in New Hampshire, was devised by the founder, Robert B. Thomas, who believed the weather was influenced by the magnetic storms on the surface of the sun, or sunspots.

The formula has been updated over the years. Predictions employ the study of solar activity, prevailing weather patterns and the atmosphere. The almanac also looks at weather trends and events by comparing past weather conditions with current solar activity.

However, many meteorologists question the almanac’s predictions and the validity of their methods. For one, the almanac’s secrecy means their methods can’t be compared with modern techniques that employ physics, math and atmospheric readings to simulate weather patterns. Such tools are used by agencies like the National Oceanic and Atmospheric Administration to build the weather reports that you see on the news or on a smartphone app on a daily basis.

Akin to the almanac, NOAA also creates seasonal outlooks on a regular basis, and it’s findings contradict the almanac. For instance, they predict below average precipitation for the Pacific Northwest and for rainfall to coat California for most of the winter. The almanac also claims a high degree of accuracy on an annual basis without releasing evidence to back the claim.

Although originally created for recording and predicting astronomical events, today the Old Farmer’s Almanac does more than predict weather patterns. Readers can also learn about gardening, recipes, the best days to fish, among other helpful tips.

For more details about this coming winter, check out the almanac’s long ranging predictions.

Editor’s note: This post has been updated to clarify that methods used by the Old Farmer’s Almanac to calculate its forecast are not considered to be scientific.