A thundershower is a short storm with heavy rainfall, lightning and thunder, and sometimes strong winds. They begin suddenly and can last anywhere from a few minutes to a few hours. These thundershowers are most common in the afternoon and evening in the summertime. They can form anywhere in the U.S. but are often strongest on the east coast, from Miami all the way up to Boston.
While rain and light wind often do not cause any delays, most airports have very strict safety guidelines involving lightning. In general, whenever there is a lightning strike near an airport (often within 5 miles) all the ground crew must seek shelter indoors. This means no baggage can be loaded onto the planes (or removed from planes for that matter), no one can guide the planes into the gates, no one can push the planes back. The planes can’t be catered (or sometimes cleaned) and they definitely can’t add fuel. Each airport sets its own guidelines but often there needs to be a period of time (around 15 minutes) without a lightning strike before ground crews can resume operations.
In the summer these thundershowers are often the biggest cause of delays. The surprising thing is that these delays can affect you even if the weather is fine where you are. The plane that will be flying you and the crew that will be working your flight might be coming from an airport that is affected by these thundershowers. If you are traveling in the summer it is best to fly in the morning before most of the weather starts. If you have to travel in the afternoon and evening you should check the weather before leaving your house. Also, you should give yourself extra time to make a connection just in case your flight is affected by these storms.