With powerful wind gusts in the forecast, city officials said they would decide just hours before the parade's 9 a.m. start whether conditions were safe enough for some or any of the event's famous balloons to float through the corridors of Manhattan.
If the answer is no, it would be only the second time the balloons have been grounded in the parade's 80-year history.
City officials said the decision will be based on information from the National Weather Service, wind-measuring instruments along the route, and their own judgment.
"You don't want to ground the balloons and all of a sudden have the wind die," said Jarrod Bernstein, a spokesman for the New York City Office of Emergency Management.
Parade organizers may be able to fly some of the balloons even if the wind is too strong for others, and the parade's floats, bands and other attractions will go on regardless of the weather.
As the clock ticked toward a decision, spectators stood in light rain and cheered as the massive balloons were spread out flat on blue carpet and inflated Wednesday evening on Manhattan's Upper West Side.
Wind gusts could reach 35 mph Thursday morning, and rain and temperatures in the 40s were forecast. City guidelines call for grounding the parade's trademark balloons, such as Snoopy and Big Bird, if winds reach 23 mph and gusts exceed 34 mph.
Those rules were put in place after 45 mph winds sent a Cat in the Hat balloon careening into a metal pole during the 1997 parade, leaving a woman in a coma.
During last year's event, two sisters, ages 11 and 26, were hurt by debris when a giant M&M's balloon snagged a streetlight. A city report said the mishap was not caused by the weather, but rather discrepancies between parade guidelines and actual conditions along the route.
Parade organizers have some flexibility in flying the balloons if the wind is strong. Some could be tethered to vehicles and essentially act as floats. The parade will also have a handful of "balloonicles" — balloons powered by motorized vehicles — that are less susceptible to wind because they are grounded.
Whatever the weather, the parade will go on with dozens of floats, marching bands, clowns, performers and celebrities.
The parade will feature 33 floats with themes as varied as Charlotte's Web and Barbie, almost a dozen marching bands from across the country, and celebrities including singers Barry Manilow, Gloria Estefan and Ciara.
John Piper, who directs the Macy's studio that makes the balloons and floats, said he is most excited for people to see a new hot-air balloon created inspired by the classic novel "Around the World in 80 Days."
"I think it's going to be just amazing," said Piper, who has been a part of the parade for 26 years.
About 600 children from Camp Broadway, for theater-loving children around the country, will perform the parade's opening number. They will be clowning, singing, tapping, drumming and dancing their way through the city.
Ten-year-old Taylor Rosenberger is performing as a clown.
"I'm excited," he said. "We actually get a float."
To protect against accidents, seven wind-measuring devices have been installed along the parade route to allow the city to monitor weather conditions during the event, Bernstein said. Police officers assigned to each balloon will be able to communicate changing conditions to the handlers, who will in turn adjust the flight pattern.
"We are able to check every location, and it will allow us to adjust how high or low to fly the balloons," Bernstein said. "I'm extremely confident that we have done a lot of work to make this parade as safe as it possibly can be."
Organizers say the Macy's balloons were grounded only once in the parade's history — in 1973 because of severe weather.