If you’re planning to light your Whistle Spliffs, cherry bombs, Ghost Rings (with or without the Afterglow Pistil), or a single whistling moon traveler this weekend, you may want to pay close attention to the weather.
From thunderstorms and lightning to trapped layers of smoky air, here are the many ways the weather could dampen — or enhance — your fireworks display.
Rain: Not a party stopper
Though it may make sitting outside waiting for the show miserable, rain, by itself, won’t dampen an explosion because fireworks burn so hot.
Many local shows around the country will go ahead in the case of rain, but lightning nearby generally means the show will not go on. Some of the biggest professional displays around the country have occasionally been called off.
In Washington, D.C., the National Park Service will cancel or delay the fireworks display if there is inclement weather, such as driving rain, high winds, lightning or low-ceiling cloud cover in the area.
This year, the nation’s capital won’t be facing these hurdles. “We’re going to have super weather here in Washington, D.C.,” said Bob Healy, a park ranger. “There’s supposed to be relatively low humidity compared to our heat wave in the prior weeks. Sunny weather, but relatively cool.”
Humidity: Blurry vision
Humidity, a measure of the amount of moisture in the air, can make it harder to light a firework. But if you do manage to get it up in the air, the humidity can dampen the colors.
Water vapor in the air can scatter the light in different directions. The more humidity, the more the light scatters, and the less visible the fireworks show becomes.
If you want to see crisp, bold colors, a fireworks display in a drier location will make the colors appear much sharper.
Humidity also allows the “boom” of fireworks to travel farther, because sound waves travel more easily through water vapor than drier air.
Dry: A dangerous spark
Drier locations make it easier to light a fuse, but they also make it easier to set off a fire that can quickly grow out of control. Recent data shows that July 4 and the day after record significantly more human-caused wildfires than any other dates.
City authorities in many wildfire-prone areas, seeing explosives as too risky, have opted to forgo the fireworks altogether and host public laser light or drone shows instead.
According to the U.S. Drought Monitor, much of the Western United States is in some form of drought this Independence Day, from the low intensity “abnormally dry” in Washington to the most severe “exceptional drought” in parts of New Mexico and Texas.
Smoke: It can linger long after the show
As the sun sets on a hot summer day, the ground’s surface cools, but warmer air remains overhead. This is called an inversion. Typically, air cools as it rises up in the atmosphere, but in an inversion, it encounters a warmer layer that traps smoke near the ground. A strong inversion can last through the night, and after a long evening of fireworks, so can the smoke.
Several studies have shown that July 4 and 5 tend to record significantly higher concentrations of particulate matter, a measure of air quality, compared with the days preceding and following the holiday.
In 2004, those were the only two days when an air quality sensor in the New York City area had unhealthy air for sensitive groups, according to E.P.A. data.
Wind: Some is good. A lot is bad.
If there is no wind at all, the smoke and smog that waft after a fireworks show will linger, reducing air quality, for a longer time.
But too much wind? That becomes a different problem.
Imagine watching a balloon rise. It rarely goes straight up, even if the wind is calm near the ground. Higher up, the wind is stronger because it is no longer being slowed down by friction against the Earth’s surface.
If the ground level is excessively windy, it will be even windier higher up where a bottle rocket or Roman candle explodes. A strong wind at that height can blow fireworks off course, creating additional and unexpected hazards, as the debris and sparks fall on areas they aren’t meant to.
Judson Jones is a meteorologist and reporter for The Times who forecasts and covers extreme weather.
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