meteorology

Tornadoes are notoriously difficult to forecast, with often deadly results: In 2011, tornadoes in the U.S. killed more than 550 people, a higher death toll than in the past 10 years combined. Now a new study of short-term climate trends offers a new approach to tornado forecasting that may give people in tornado-prone regions as much as a month of forewarning that twisters may soon be descending.

On March 14, 2008, at 9:38 p.m., something happened in Atlanta that had never happened in the city’s 171-year history: A tornado ripped through a 10-kilometer-long swath of the city’s downtown. The twister, with winds reaching 210 kilometers per hour, blew out skyscraper windows and stalled a major college basketball conference tournament.

Predicting the weather has been central to human civilization since the Babylonians started studying cloud patterns in 650 B.C. The key to weather predictions is making correct assumptions. Today, instruments like Doppler radar that measure rainfall work under the assumption that raindrops fall at their terminal velocity. A new study, however, shows that some raindrops fall faster than they should, indicating rainfall instruments — and by extension, weather forecasts — may need some tweaking.

Two hundred years ago, a sea captain was sailing in the Azores, a Portuguese archipelago in the middle of the Atlantic Ocean, when he observed “an immense body of smoke rising from the sea.” As he watched, the smoke, from a volcanic vent offshore of the island of St. Michael’s, began to rotate on the water “like a horizontal wheel,” the captain wrote in his 1811 account of the event. The rotating smoke and ash grew into a dark column and ascended high into the sky, spawning waterspouts and flashes of lightning.

A huge thunderstorm was gathering above central Oklahoma on May 20, 1977. As the storm intensified, a tornado began to form and struck the ground, leaving wreckage in its path. Although the tornado itself is now well-known, the forces behind its formation are still surprisingly sketchy. Using high-resolution modeling, however, a new study reveals how some atmospheric conditions can make tornadoes more — or less — likely to form.

As residents of Galveston, Texas, scramble to evacuate before Hurricane Ike makes landfall tonight, most Houston residents have been told to stay put. But even Houston — about 130 kilometers (80 miles) to the northeast — is in for some extreme weather tomorrow.