A neutronic storm was a plasma energy storm which could travel through space at faster-than-light speeds. These storms were saturated with radiolytic isotopes, which were harmful to a number of species, including Humans and Vulcans. They also contained plasma eddies.
Around the mid-21st century, the Vulcan starship T'Plana encountered a class 5 neutronic storm. Unable to outrun the storm's wavefront, the ship was destroyed and all crewmembers were lost. (ENT: "The Catwalk")
Sometime during the mid-22nd century, the ECS Horizon ran into a class 3 neutronic storm. According to Travis Mayweather, the crew took shelter in the ship's core for six weeks, and during that time, the ship's generators went down, and they lost the grav-plating and life support. (ENT: "The Catwalk")
In 2152, the Earth Starfleet vessel Enterprise NX-01 encountered a class 5 neutronic storm that spanned more than half a dozen light years in diameter. Unable to outrun the wavefront, which was traveling at high warp, the Enterprise crew was forced to take refuge in the catwalk of one of the ship's inactive warp nacelles to prevent exposure to the deadly radiolytic isotopes. Enterprise herself would be protected from destruction since the crew reinforced her structural integrity. A command area was set up in one of the nacelle's compartments, and the crew was able to steer through the wavefront with little trouble. Enterprise was finally able to leave the storm nearly eight days after entering the wavefront. (ENT: "The Catwalk")
Mayweather later mentioned the encounter with the storm in a letter to his sister. His sister then told their mother, Rianna, of the incident, referring to it as a "close call". Mayweather assured his mother that it wasn't that bad and his sister likely made it sound worse than it was. (ENT: "Horizon")
In 2376, Dala (while impersonating Captain Janeway) informed two Telsian miners that they had to leave orbit without paying them for their bolomite because a neutronic storm was approaching and interfering with their transporters and communications. (VOY: "Live Fast and Prosper")