with flat anvil-like cirriform top caused by wind shear where the rising air currents hit the inversion layer at the tropopause. Mamma or mammatus: consisting of bubble-like protrusions on the underside. Tuba: column hanging from the cloud base which can develop into a funnel cloud or tornado. They are known to drop very low, sometimes just above ground level. Flanking line is a line of small cumulonimbus or cumulus generally associated with severe thunderstorms. An overshooting top is a dome that rises above the thunderstorm; it is associated with severe weather. Precipitation-based supplementary features Rain: precipitation that reaches the ground as liquid, often in a precipitation shaft. Virga: precipitation that evaporates before reaching the ground. Effects Cumulonimbus storm cells can produce torrential rain of a convective nature (often in the form of a rain shaft) and flash flooding, as well as straight-line winds. Most storm cells die after about 20 minutes, when the precipitation causes more downdraft than updraft, causing the energy to dissipate. If there is sufficient instability and moisture in the atmosphere, however (on a hot summer day, for example), the outflowing moisture and gusts from one storm cell can lead to new cells forming just a few kilometres (miles) from the former one a few tens of minutes later or in some cases hundreds of kilometres (miles) away many hours later. This process cause thunderstorm formation (and decay) to last for several hours or even over multiple days. Cumulonimbus clouds can also occur as a dangerous winter storms called "thundersnow" which are associated with particularly intense snowfall rates and with blizzard conditions when accompanied by strong winds that further reduce visibility. However, cumulonimbus clouds are most common in tropical regions and are also frequent in moist environments during the warm season in the middle latitudes. A dust storm caused by a cumulonimbus downburst is a haboob. Hazards to aviation Cumulonimbus are a notable hazard to aviation due most importantly to potent wind currents but also reduced visibility and lightning, as well as icing and hail if flying inside the cloud. Within and in the vicinity of thunderstorms there is significant turbulence and clear-air turbulence (particularly downwind), respectively. Wind shear within and under a cumulonimbus is often intense with downbursts being responsible for many accidents in earlier decades before training and technological detection and nowcasting measures were implemented. A small form of downburst, the microburst, is the most