Cloud suck The telltale signs for a pilot climbing in the thermal under a "sucking" cloud are (1) lift strengthening, (2) lift getting smoother, and (3) widening of the thermal. Paraglider pilots have reported being unable to descend in strong cloud suck, even after bringing their canopies into deep spiral, which would normally result in a rapid vertical descent. Cloud suck is especially dangerous for paraglider pilots, whose maximum speed is less than 30 knots, because storm clouds (Cumulonimbus) can expand and develop rapidly over a large area with accompanying large areas of strong lift. On 14 February 2007 while practising for
Cloud describes the occasional arrangements of cloud structures into particular patterns that are discernible by a surface-based observer (cloud fields usually being visible only from a significant altitude above the formations). These varieties are not always present with the genera and species with which they are otherwise associated, but only appear when atmospheric conditions favor their formation. "Intortus" and "vertebratus" varieties occur on occasion with cirrus fibratus. They are respectively filaments twisted into irregular shapes, and those that are arranged in fishbone patterns, usually by uneven wind currents that favor the formation of these varieties. The variety "radiatus" is associated with