DRY INTRUSION

(or 'dry slot') -- A narrow region, virtually cloud-free which separates a baroclinic leaf (q.v.), and the adjacent frontal cloud. This region is the result of abruptly descending upper tropospheric/lower stratospheric air into a rapidly developing and potentially damaging low pressure system -- hence the low humidity content/absence of cloud. Water vapour imagery in particular is used to diagnose this feature, and the rate of 'darkening' of the dry slot gives a clue to the rate of development of the whole storm complex.