How Convectional Rainfall is Caused

Is it not amazing to see a beautiful sunny day turn into a ominous deluge in mere minutes? Have you ever watched big puffy clouds lazily meandering across the sky turn into monstrous, boiling clouds crackling with energy? These types of storms are caused by two different air temperatures mixing in the upper atmosphere to cause convectional heating, creating monster storms that bring massive rainfall.

Convection is the process in which warm air, which is less dense than the cool air, is forced to rise into the atmosphere as the cold air descends. When the sun heats up the ground, moisture evaporates and rises into the atmosphere on the currents of the ascending warm air. On the ground, we feel the effects of this process; It is known as humidity. As the warm, humid air rises higher, it begins to cool as it ascends until it reaches the condensation point. The condensation point is the point when the water vapor begins to turn back into liquid form, resulting in clouds. As the warm air continues higher into the atmosphere, the clouds begin to grow and become heavy, laden with rain.

When the clouds grow to a height of 10 to 20 km, they are known as cumulonimbus clouds. These are the towering, foreboding clouds that are laden with water droplets. At this elevation, the water droplets begin to freeze. When the frozen pellets and unfrozen water droplets begin to collide due to the chaotic atmosphere inside the cumulonimbus cloud, the air becomes electrically charged and lightening is then formed. This building-up process can be quick, or it can take hours and even days. Generally, the more time is given to the evaporation part of the convection process, the greater the strength of the storm.

Convectional rainfall is probably the most common form of rainfall around the world. The most severe examples of convection storms can be found in the tropics, where there is plenty of water and warm air. Hurricanes and typhoons are both caused by convection heating of the air over a period of days or weeks. Because of the amount of time that these storms take to build, massive amounts of water are drawn into the atmosphere, resulting in the devastating deluges that are associated with these types of storms.

Storms created by convection heating are called air-mass storms. These are the pop-up storms that occur in regional areas. Unlike orographic or frontalthunderstorms which can cover large regions, convection storms usually only cover an localized area. Tornado spawning supercells are caused by the convection process.

So, the next time that you are out with your family and you notice the clouds building up, it just maybe a good idea to find some shelter. When it comes to convection rainfall, it’s hard to tell just how wet you might get.