Will It Rain on Your Wedding Next Year?

LONDON, June 23, 2009 -- Predicting the weather is a notoriously tricky business. For all the new technologies at their disposal -- Doppler, satellite imaging, computer mapping -- weather forecasters can sometimes seem less accurate than grandpa with his bum knee. And that's for tomorrow's weather.

But what about the weather next week -- or next month -- or next year?

On May 29 in London, the maverick long-range weatherman Piers Corbyn called a news conference and informed the world that in about a month, certain parts of the United States were going to be very bad for picnicking.

"June 22 to June 24, this is for the U.S.A," said Corbyn, whose professional kit includes a 20-year-old calculator, a globe held together with Scotch tape and a sun made out of a shopping bag. "A very wide region, really. Major thunderstorms and local floods with devastating tornadoes, very damaging, killer tornadoes, I think would be a fair description. ... Oh yes, hail as well."

Fast forward three-and-a-half weeks -- to today. There's damaging hail in New Jersey. There are tornados in Colorado. A few days earlier than predicted, but just a precursor, Corbyn later explained, to the imminent main event.

By Zeus, Corbyn was just about right.

"We can predict extreme events a year ahead," Corbyn told "Nightline." "What we can do will help the world."

Watch the full story tonight on "Nightline" at 11:35 p.m. ET

The "we" is Corbyn and a handful of colleagues who trawl world weather reports from years past, looking for patterns that might be repeated.

Over the past 13 months, Corbyn has predicted nine extreme weather events in the United States, including ice storms Jan. 6-8 in the Northeast and the Midwestern blizzards of Feb. 3-6. Corbyn claims to have been right eight-and-a-half times out of nine.

How do you get half of an event right?

"Well, it's because the event happened but the location was -- was a bit out," he said.

Storms that thrashed Britain in November 2007 were predicted by Corbyn 11 months before they happened.

"We are unique and revolutionary," Corbyn said. "And we have a skill which is completely beyond the possibility of standard meteorology."

Weatherman: 'Charged Particles' From Sun

The details of Corbyn's forecasting technique -- he calls it the Solar Weather Technique -- are locked in a bank vault, he told "Nightline." He did offer a broad outline of his process.

Corbyn looks at solar activity, and the heating or cooling of the stratosphere, and asks what impact those changes will have on weather systems. He looks for patterns in history that may repeat themselves. He studies the cycle of magnetism on the sun and the eclipse cycle of the moon.

"The weather is not driven just by what's happened in the weather recently," Corbyn said. "It's driven by what's happening on the sun. ... Especially the charged particles, which come from the sun."

A physicist by trade, Corbyn made his first weather predictions 20 years ago. He placed bets based on his predictions. He didn't always win.

"We had a June some years ago when we said there was going to be snow in June," he told "Nightline." "Yeah, yeah, yeah, we did say that."

Corbyn has honed his skills over hours spent in his tiny office. Apparently, bookmakers now refuse to take his bets.

"We were making too much money," he said, "so they stopped us."

These days, farmers like Geoff Phillpot buy Corbyn's forecasts.

"It is amazing how accurate he can be on long-range," said Phillpot, standing in a field of plump cauliflowers. "He predicted, for instance, this year it was going to be very cold, the coldest part of the winter was going to be Jan. 6-9.

"We were able to utilize our knowledge and cut our cauliflower that were at risk at that time and cut them in advance and cut them very tightly, so the damage was negligible," he said.

Corbyn does have his detractors.

"I'm not saying that Corbyn's method is flawed. In fact, he probably does have some glimmers or grains of truth and reality in what he says," Accuweather.com director of forecasting operations Ken Reeves told ABC News.

However, Corbyn's concentration on solar activity for his predictions does invite criticism, Reeves said.

"The problem is, there are far more environmental factors that are involved than just one feature," he said.

Reeves also questions Corbyn's ability to consistently produce accurate forecasts.

"Can someone potentially hit a storm, to the day, from 11 months out?" he asked. "Yeah, they could, but realistically, advancement of science isn't at a point where you can do that reliably."

Corbyn is also a global warming denier, automatically qualifying him as a crank to some critics. And he's very secretive about his methods, placing them beyond the scrutiny of science.

That's about to change, he said.

"Later on this year, we're going to reveal key aspects of the Solar Weather Technique -- in October, Oct. 28 this year," Corbyn said. "Because we think at some point, the world does have to know."

Weatherman: Should I Plan a Vacation?

When "Nightline" interviewed Corbyn May 29, all we wanted to know was: Would the sun shine for a correspondent's family vacation in Cornwall in early June?

"We expect that period, the 6th to 9th or so, to be part of a solar weather impact period around the world, which will see a lot of thundery developments in a lot of places and one of those is very likely to be Cornwall," Corbyn said.

Undaunted, we packed the sunscreen and headed out.

But this time Corbyn was right. Driving to Cornwall June 6, the car's windshield wipers struggled to cope with a deluge. Roads were flooded. The sunscreen was not required.

The weather, it turned out, was dreadful.