What finally produces a tornado from a supercell?
The answer is still not clear, but field work in the 1990s yielded some important clues. NCAR joined a number of agencies and universities in 1994–95 for a project called VORTEX. Instrument-studded cars and aircraft, along with portable Doppler radar, captured the life cycle of several tornadoes in detail. The data, which are still being analyzed, hint that a strong downdraft at the rear of a supercell may combine with the storm’s intense updraft to produce small-scale wind shear that may be key to a tornado’s development. Tornadoes vary tremendously in appearance. Even the same funnel cloud can look different when viewed at different times or from different angles. Many tornadoes emerge from a wall cloud, a rotating cloud hanging from a rain-free part of a supercell. However, most wall clouds do not produce tornadoes. In arid or semiarid climates, a tornado funnel may look clear or translucent even when the circulation extends fully to the ground. Large tornadoes may resemble a cloud
