Here's what Accuweather says the conditions will be like for July 4 fireworks:
A large part of the United States will escape nature’s fireworks ruining shows on Wednesday evening, but steamy air is expected to remain in firm control from the Plains to the East.
Most of the widely separated thunderstorms that dot the Great Lakes and Northeast during the day on July Fourth may dissipate before the evening fireworks displays. Warmth and humidity will remain, creating sticky conditions.
One potential problem may be where calm winds prevent smoke from quickly clearing out, which can make fireworks later in the shows more difficult to view.
The higher the humidity, the duller the colors the fireworks can be.