Winds greater than 23 mph and gusts of 34 mph would keep SpongeBob, Snoopy, Pikachu and the rest of Macy's helium-packed behemoths firmly on the ground.
New York officials set guidelines on balloon size and wind speeds after a Cat in the Hat balloon struck a lamp post on Central Park West in 1997, knocking loose a piece and injuring four people, including a woman who spent more than three weeks in a coma. In 2005, an M&M balloon knocked a light pole on two sisters.
"Winds are going to be critical," said Chris Vaccaro, a spokesman for the National Weather Service.
Thursday's forecast calls for northwest winds in the 14 to 24 mph range, with gusts up to 40 mph, said Vaccaro.
But at least one official was optimistic the balloons would be allowed to fly.
"It looks good. It looks very good," said New York Police Department Patrol Chief James Hall, who will make the call.
The decision on floating the 16 giant balloons will be made early Thursday, according to a statement from Macy's: "A determination is made on their inclusion based on real-time weather data on parade morning and not forecasts, so it's not helpful to discuss it now."
Others -- from New York's police commissioner to travelers visiting the city for the parade -- were discussing it.
"We came all the way from Puerto Rico to see the parade," Jose Ramirez, standing with his sons on the parade route, told CNN. "It would be a disappointment if we can't see the balloons."
One holiday tradition related to the Thanksgiving Day Parade will go on as planned -- the parade-eve inflating of balloons in the vicinity of the American Museum of Natural History on Manhattan's Upper West Side.
"The balloons aren't about Thanksgiving," said Michellian Findley. "It's about fellowship, family and just being thankful."
Only in New York would each giant parade balloon be assigned a police sergeant as an escort to measure wind speed and conditions.
"We've had several meetings," Police Commissioner Ray Kelly said. "We have instruments that give us the crosswind measurements. We've done a lot of training on this."
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