Tue 11 Jun
Sky Mountains
Why clouds don't crash

An average cloud carries hundreds of tons of liquid water and ice, snow or hail. What keeps all this water weight suspended in the cloud? The answer is because they float in the clouds updrafts. Updraft currents in a cloud body are caused by convection. In a typical cumulus cloud the average drop size is around 0.01mm, weighing 0.01 grams. A drop this size falls at less than 0.5cm per second, thus just the slightest updraft is sufficient to suspend droplets or crystals of this size.

Larger droplets fall faster and 'solid' droplets, like hail, can reach a speed of more than 100km per hour (60mph). Therefore strong updrafts of many Meters per second are required to suspend large raindrops or hail in a cloud.

Precipitation sized particles typically larger than 0.1mm often fall from a cloud. Entering the drier air below the cloud base, they are loosing weight again by evaporation. Sometimes they even evaporate completely. The cloud itself can survive precipitation falling from its base provided that updrafts continue to promote condensation within the cloud.

Downward air motion will quickly dissipate a cloud, as the air compresses and air temperature Increases, which causes cloud droplets to evaporate.