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.