Image: Fireworks over Chicago
Kiichiro Sato  /  AP
Fireworks explode over Chicago and Lake Michigan on July 4, 2010.
updated 6/30/2011 10:40:29 AM ET 2011-06-30T14:40:29

America's Independence Day couldn't be better timed. It falls in early summer, when the days are usually hot and clear and the nights are comfortably warm.

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That's perfect weather for parades, family gatherings, baseball games, picnics, barbecues, corn on the cob, and — after dusk — fireworks. Certainly our Founding Fathers planned it that way!

Good weather is the key to these good times, of course, but did you know it's also the key to spectacular fireworks?

Nothing puts a damper on a fireworks display like a muggy day. Let the chairman of the famed Zambelli Fireworks Company of New Castle, Pa., explain: “The brilliance of fireworks is better in low humidity," says Dr. George Zambelli. "The higher humidity will cause the smoke to lay closer to the ground and appear more dense, and ultimately it will decrease the brilliance.

"The most brilliant fireworks are in low humidity when you have the winds carrying the smoke away from the spectators. In large displays you have a lot of pyrotechnic material going off at once, so you need something to dissipate that smoke,” he said.

What about other weather conditions?

Lightning storms can be too dangerous to set fireworks off, and they usually cause a delay in the program.

Oddly, rain isn't a problem. Fireworks can be fired right through it.

"Rain doesn't cause an issue and it doesn't impact how fireworks look because the colors are so vibrant," says Julie Heckman, executive director of the American Pyrotechnics Association, the fireworks industry's main trade association.

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Wind, on the other hand, can be a problem — especially if it affects the safety of spectators.

"Winds will change the direction of where the fallout is," Heckman said. "Winds are typically monitored all day long up until they push the fire button on fireworks shows. When winds exceed 20 to 30 miles per hour, fireworks companies won't shoot [the shows] off."

Shows can also be canceled because of overly dry conditions and the fire danger posed by falling sparks.

Several shows this year already have been scrubbed for this reason. The fire chief in Flagler County, Fla., has canceled all shows in that area because of tinder-dry conditions. Fourth of July shows in parts of drought-stricken Texas and fire-ravaged Arizona also have been scratched.

Fireworks specialists look for a few key weather elements to fall into place for the perfect show.

PhotoBlog: View, discuss weather photos

"The optimal weather conditions for fireworks displays are high ceilings, low humidity and light winds that are moving in the opposite direction from the spectators," Dr. Zambelli said.

As America's Independence Day 2011 approaches, we've listed fireworks celebrations in some major cities. Check the forecast link to see what kind of viewing conditions you can expect.

New York City
Location: 24th to 50th streets on the Hudson River
Time: 9:20 p.m.
See: Forecast

Location: Esplanade
Time: 10:30 p.m.
See: Forecast

Location: Philadelphia Museum of Art, Benjamin Franklin Pkwy.
Time: 8:30 to 11 p.m.
See: Forecast

Washington, D.C.
Location: National Mall
Time: 9:30 p.m.
See: Forecast

Location: Navy Pier
Time: 9: p.m.
See: Forecast

Los Angeles
Location: Rose Bowl Stadium, Pasadena
Time: 9:05 p.m.
See: Forecast

Location: Centennial Olympic Park
Time: 9:40 p.m.
See: Forecast

St. Louis
Location: Gateway Arch
Time: 9:15 p.m.
See: Forecast

Location: Lake Union
Time: 10 p.m.
See: Forecast


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