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. The outer barrier of a neutronic storm was known as a neutronic wavefront (Borg classification 3472 - particle density anomaly).
Over a century later, the Earth Starfleet vessel Enterprise encountered a neutronic storm near Takret space 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. The Enterprise herself would be protected from destruction since the crew reinforced her structural integrity.
Setting up a command center in one of the nacelle's compartments, the crew was able to steer through the wavefront with little trouble. While the ship was within the wavefront, however, it was boarded by members of the Takret Militia who were searching for three deserters who had been brought aboard Enterprise. The Takret themselves were immune to the radiation in a neutronic storm and thus could roam the ship freely. The Enterprise crew was able to drive the Militia officers away by steering the ship towards a plasma eddy. Following this incident, the Enterprise was able to leave the wavefront earlier than expected thanks to the piloting skills of Ensign Travis Mayweather. (ENT: "The Catwalk")
Mayweather later mentioned the encounter with the wavefront 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 the USS Voyager encountered a class 9 neutronic wavefront, which was expanding at 200,000 kilometers per second. Voyager was unable to escape the wavefront at warp speeds as the neutron radiation was disrupting plasma flow within the ship's systems. Unable to escape the wavefront at impulse power, Voyager generated an inverse warp field in order to lock itself in position, inoculated the crew against the expected radiation increase, and attempted to ride the storm out. (VOY: "Fair Haven")
That same year, 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 communications. (VOY: "Live Fast and Prosper")