How Far Ahead Can We Predict the Weather?

Can we really predict the weather three months out?

One of the country's leading commercial forecasters, AccuWeather, said earlier this month that it could predict the weather conditions and temperature three months ahead of time. It's a bold claim that has been refuted by some meteorologists who say such a 90-day forecast will only be as good as historical averages and not much use to someone planning a hike or outdoor wedding this summer.

That's because the Earth's atmosphere is a chaotic system that doesn't follow an easily predictable path, according to Keith Seitter, executive director of the American Meteorological Society in Boston.

"If anybody kept track about how (AccuWeather) did, they would find it's a pretty horrible forecast," Seitter said.

The best weather forecasters can do now is seven to 10 days. After that, accuracy drops off quickly.

The good news is that forecasting has gotten better over the years. Improvements in computer technology, data collection and weather models have improved this forecasting number about one day each decade.

One of the biggest advancements has come in boosting computer power. The National Oceanic and Atmospheric Administration, the parent agency of the National Weather Service, operates supercomputers in Reston, Va., ("Luna") and Orlando, Fla., ("Surge") to come up with weather forecasts.

After a $44 million upgrade in January, each one has the capacity of 2.89 petaflops, or 2.89 quadrillion calculations per second, according to Richard Michaud, director of NOAA's office of central processing. That's up from 778 teraflops (1 petaflop equals 1,000 teraflops) of computing power last year.

In simpler terms, it means that the faster, bigger computers will allow the agency's scientists to:

Better predict the amount, timing and type of precipitation in both winter storms and thunderstorms Create "water forecasts" and more accurately predict drought and floods Connect the air, ocean and waves to track eight hurricanes at once These supercomputers are the brains behind the weather forecasts you see on TV each night or your smartphone when you wake up.

"We collect trillions of observations per day, then we create a state of the atmosphere," Michaud said. "Then we run weather models to forecast into the future."

But Michaud cautions that the upgraded supercomputers still won't be able to push out an accurate local forecast months ahead.

Forecasts are getting better, just not longer.

"Its not just about adding more computing time," he said. "You have to have the appropriate way to assimilate the data into the models."

Building better models is the work of computer scientists, climate scientists and meteorologists.

In this instance, the European forecast model (which includes forecasts for both the United States and Europe) has a slight advantage over the U.S. weather model. That's because the European weather agency has fewer weather-related forecasts to produce, according to Seitter, so they can focus more effort on one product.

"Every time the U.S. model gets better and is running close to the European model, they get an infusion of computing power," Seitter said. "We have always been lagging a tiny bit."

In the future, NOAA's Michaud says that advances like quantum computing and new kinds of processors could make a difference extending long-range forecasting. But there will always be limits that can't be overcome, said AMS's Seitter.

"The atmosphere itself doesn't know what it's going to do a month from now," Seitter said. "It does have predictability in a probabilistic sense. You can say is it wetter or dryer than normal in the next three months. What you can't do is say today that it is going to rain in 42 days and then be sunny after that."

A record-setting El Niño has been affecting weather around the world for months. It's brought much-needed rain to California, for example, but also boosted hurricanes in the Pacific and amplified the effects of drought in Indonesia, fueling massive wildfires. And though the surface temperatures may have peaked this fall, the effects on the atmosphere may be most acutely felt in the spring. Here we look at a some of the dramatic effects of the

El Niño–Southern Oscillation


In Indonesia wildfires burned thousands of acres during the fall. El Nino conditions led to dry forests, which exacerbated the risk of fires spreading out of control. Pictured: Haze shrouded Indonesian cities for months.

"During El Niño years, rain that is normally centered over Indonesia and the far western Pacific shifts eastward into the central Pacific; as a result, parts of Indonesia experience drought," reports

NASA's Earth Observatory

. The lack of rain worsened fires that Indonesia's government said were intentionally set by plantation companies to clear land for palm oil cultivation and, ironically, tree plantations.

Indonesia Fires Choking People, Threatening Wildlife

In early December, Chennai, a city in India, saw an El Nino-inspired deluge, receiving more rain in one day than any other since 1901. This was preceded by a month of monsoon rains in the Indian state of Tamil Nadu that were well above normal,

according to NASA


Above, fresh snow sits on the San Gabriel Mountains in the Angeles National Forest at sunset. A series of powerful storms intensified by El Nino hit Southern California during the first week of the year.

El Niño Makes A Late Appearance

Above, a surfer takes advantage of the high surf during near the entrance of Santa Barbara harbor.

Work crews in San Diego diverted a gas line near a large sink hole that developed near a sea wall after heavy rain runoff near the La Jolla Beach and Tennis Club at La Jolla Shores.

A man got a wet surprise as high surf from storms in California crashed into a wall and spilled onto a road in Montecito. El Nino typically intensifies storms in the Pacific and leads to a gentler Atlantic hurricane season.

El Nino Messes with Earth in Weird Ways