a small-scale but intense core of strong winds, usually within (and moving quickly along) a well-defined jet stream (See main FAQ Q/A 2A.1). They generally do not have a length much more than two to three-hundred kilometres, and can be associated with explosive cyclogenesis events (q.v.). Difficult to pick up via conventional observations (e.g. radiosonde wind-finding), but can be detected in WV imagery. (See also Q/A 2A.8)