Meteorologists Are Not Happy About AccuWeather’s New 90-Day Forecast

April 21, 2016 | Joanne Kennell

Photograph of a wall of clouds in Oklahoma
Photo credit: Jonathan C. Wheeler/flickr (CC BY 2.0)

"These forecasts are actually even worse than the Farmer’s Almanac.”

Last week, AccuWeather, a large American media company that provides commercial weather forecasting services worldwide, introduced 90-day forecasts. The move has many meteorologists fuming — they assert that predicting weather patterns more than 10 days in advance is pretty much pointless.

This is not the first time AccuWeather has unveiled completely unscientific forecasts. Before this stunt, AccuWeather’s longest-range forecast was 45 days, and those predictions were dismissed as "not rooted in any science currently available to meteorologists and have not demonstrated value" by The Washington Post back in 2013.

And yes, while improvements in modern-day technology coupled with weather-predicting supercomputers have in fact made weather forecasts more accurate — a 5-day forecast today is just as accurate as a 3-day forecast back in 1995 — just how far into the future can a forecast actually predict?

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To make it perfectly clear, it is NOT 90 days.

In fact, the longest we can trust a forecast with some degree of certainty is 10 days, which is pretty spectacular given everything that is involved in forecasting the weather.

There are a lot of people who believe forecasting the weather is easy, and being a meteorologist myself, trust me, I have heard all the jokes — some of which are actually quite amusing. However, there are a massive number of variables that makes forecasting the weather so difficult, and the more time that passes, the less likely the predictions will be accurate.

To create a weather forecast, meteorologists combine information about current weather conditions and apply what we know about atmospheric dynamics and flow, what the weather has done in the past, and examine several advanced computer simulations. Incorporating all of this information, meteorologists use their knowledge, training, and instincts to develop a weather forecast.

However, the weather is very chaotic or “stochastic,” and it is a prime example of the butterfly effect — how one small change today can ultimately lead to a massive difference 90 days later. AccuWeather does recognize this nature of weather, and posted this disclaimer about their new long-range forecast: "People should not use long-range forecasts as a strict guide, but rather look at how the weather patterns evolve."

But truthfully, the forecasts can’t be trusted at all, according to US meteorologist Dan Satterfield, who writes about atmospheric science for the American Geophysical Union. "We are in the realm of palm reading and horoscopes here, not science," he said in a blog post.

"These forecasts are actually even worse than the Farmer’s Almanac, since they give rain chances and temperatures for exact points months into the future! This kind of thing should be condemned and if you have an AccuWeather app on your smart phone, my advice is to stand up for science and replace it."

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