Strong Winds May Ground Biggest Balloons at Thanksgiving Day Parade Sonic the Hedgehog might not appear in the Macy's Thanksgiving Day Parade if the weather creates hazardous conditions. The fate of the world's most famous balloons is up in the air. There will be marching bands from across the country, clowns toting confetti catapults and floats carrying chart-topping musical stars when the 87th Macy's Thanksgiving Day Parade makes its way down Central Park West on Thursday. But weather predictions calling for strong winds mean that Snoopy and his helium-filled pals might not make it. Winds of at least 23 miles per hour are expected on Thanksgiving Day, with gusts up to 45 m.p.h. expected, according to the National Weather Service. After a Cat in the Hat balloon hit a lamp post at West 72nd Street and Central Park West in 1997, knocking a portion down and injuring four spectators, an investigation led to city guidelines that stipulate maximum balloon sizes and wind speeds. If the wind blows at 23 m.p.h. or more, and gusts reach 34 m.p.h., SpongeBob and the biggest of his inflatable brethren will be grounded. The decision on floating the big balloons will be made by several agencies, based on weather conditions Thanksgiving morning. The nightlong ritual of inflating the balloons, on West 77th and West 81st streets, will go on, said John Piper, the vice president of Macy's Parade Studio, who works year-round crafting the balloons with a full-time team of 26 in Moonachie, N.J. But if the wind howls as predicted, they won't be paraded. The balloons will be unzipped and deflated, folded up right there on the Upper West Side and sent back to New Jersey. The wind rules only apply to the group of 16 giants, like Pikachu and Spider-Man. The less celebrated, smaller balloons, like a baseball and a smattering of star shapes, still have a chance if the weather gets bad. Should the biggest balloons launch, each would be assigned a police sergeant, equipped with monitors to measure the wind speed during the parade, along with the usual team of handlers. "We've done a lot of training on this," said Commissioner Raymond W. Kelly. Mr. Kelly himself has firsthand experience: As a teenager he manned the ropes of a giant turkey balloon while working for Macy's, long before the wind rules were drawn up. "Those were the days when you really had to hold on," said Mr. Kelly, 72. The only time the giant balloons were grounded was in 1971, according to a spokesman for Macy's. Accidents, possibly wind-related, have occurred, including a 2005 incident when a listing M&M balloon took down a light pole, injuring two sisters. In a similar episode, in 1993, Sonic the Hedgehog caused an accident that left an off-duty Suffolk County police captain with a broken shoulder. Despite the risks, many hope the famous characters make it aloft. "It's going to be a very sad day if the balloons don't even make it down the street," said Murray Potash, 69, an accountant from Plainview, N.Y., who is taking his grandchildren, Reese, 6, and Casey, 4, to their first Thanksgiving parade. But, he added. It will give me more of a desire to wait for 365 more days to go back and be there again. You have to see the balloons once before you die.