Southern Big Horn County and northwestern Washakie County are under a tornado warning until 12 p.m., according to the National Weather Service in Riverton.

Shortly before 11:30 a.m. Friday, a severe thunderstorm capable of producing a tornado was located 18 miles south of Otto, or 23 miles southwest of Basin, moving east at 25 mph.

Rotation was indicated by radar, the National Weather Service says.

The thunderstorm will remain over mainly rural areas of southern big horn and northwestern Washakie Counties.

People in the area are urged to take cover inside a sturdy building and avoid windows.

Flying debris will be dangerous to anyone caught without shelter.