Citing severe weather late Monday afternoon, Montgomery County firefighters suspended the search for a 19-year-old man who went missing while swimming in the Potomac River in Great Falls, according to a spokeswoman.

The official, Beth Anne Nesselt, said the search would resume once the weather clears. Authorities said at 5:30 p.m. that they were trying to decide whether they would search after dark. The National Weather Service has issued a severe thunderstorm watch in the county until 10 p.m.

The teenager went missing about 2:30 p.m. off Purple Horse Beach, near Old Angler’s Inn, where the Billy Goat Trail crosses Bear Island. It is one of the most rugged sections of the trail, and Nesselt said that going into the water, even to wade, is prohibited because of strong currents.

Nesselt said the swimmer was among four that went out. Three managed to return. Authorities had been searching by foot, boat and helicopter.

The search began about two and a half hours after firefighters helped rescue four people who had fallen from a raft on the Potomac River in roughly the same area. Officials said 10 people were on the raft, and four went into the water. Three managed to get to shore and rejoined their group; a fourth was taken to a hospital with unspecified but minor injuries.