Are long range forecasts accurate?
A lot of people ask me about long range forecasts as we head into the summer months, winter months, and even into the spring months. Will it be colder than usual? Could it be a wet summer? Will next winter give us snow?
One traditional way of getting a long range forecast is by picking up the Old Farmer's Almanac. It has been around since 1792. They claim they use a secret formula that takes into account of solar activity, basic climatology, and forms of meteorology to forecast a year’s worth of weather. They also claim they have an 80 percent accuracy when it comes to accurately predicting the weather in the long range. The secrets to their formula are secretly stored in a vault/black box (based on their website). This is all true.
You might ask weather or not the old farmers almanac or even the farmer's almanac is accurate. The answer? Not really. Very little science involved.
Here was the Farmer's Almanac forecast for this past winter:
The Farmer’s Almanac predicted that the 2016-2017 Southeast winter would be "penetrating cold and very wet”. Instead, we ended up with our fifth warmest winter ever recorded. Yes, NOAA and National Hurricane Center will put out long range forecasts, but they use some science by recognizing weather patterns like El Nino, La Nina, and recognizing how cooler or warmer areas of water in the Northern Hemisphere can translate to our weather patterns.
For instance in most cases, El Nino years will give us cooler and wetter winters, but not all the time. It is hard enough to predict weather a week away. We are pretty good with forecasting weather in three to five days, but it gets a little difficult after seven days. It is far easier to forecast a system that has already developed versus a system that has NOT developed. A storm that forms fifty miles north can change a forecast drastically, especially if it involves winter precipitation.
Farmers, in particular, would love to have long range forecasts to help prepare their crops during the growing season. Droughts, floods, freezing temperatures, and brutal heatwaves can have a big impact on production. While the (Old) Farmer’s Almanac can be a good tool to get an idea when the weather will change, it is likely based on climatology. For instance, we expect our summers to be hot, sometimes muggy, and the small chance for an afternoon thunderstorm. If you ask me what the weather will be like on July 16, that would be my generic answer to you.
Our weather models can be pretty good within seven days, but the science is simply not there (yet) to forecast specific weather events two weeks out or later.