How Precipitation Forms

For precipitation to form, we need four key ‘ingredients.’ First, we need a lifting mechanism.  This will create saturation. There are three commonly known ways to create this uplift. 
 
The most common one is a front, also known as a cyclone. . These are large scale weather patterns that can last from hours to even  days. An everyday example of this type of weather pattern is when a warm front moves into a surface cold front. The warm air will try and stay on top creating a ‘lift’ for saturation to form. The next common way is through convection. This happens in deep cumulonimbus clouds and usually only lasts for an hour or two. These will form mostly in the summer, and are known as thunderstorms (like the ones we see in the summertime in Albany, New York.) Lastly, orographic lifting is another way to get lift and saturation. This happens when there is a mountain range, on the windward side of the mountain. The air will rise on the windward side, and, while it rises, it results in adiabatic cooling and condensation. Which is a “condition is which heat does not enter or leave the system.”
 
Now after we have the lifting part, we need the next few steps: water vapor to condense and grow. We’ll want the air to reach 100% relative humidity, and from here, it depends if it is a clean water particle, or not. If it is a clean water particle, then it will have to find some cloud condensation nuclei to form onto, and then it can grow. Cloud condensation nuclei (or CCN for short) are particles such as sea salt, dirt, aerosols, or minerals and they serve as a base for water droplets to form onto. A clean water droplet will have a hard time forming to another water droplet, unless it has a CCN, which will allow for it to initiate condensation. (If you have a “dirty” water particle, that just means it’s already mixed with a CCN and doesn’t need to find one to form!) Usually, if it is “dirty” air, it will have lots of small cloud droplets (water droplets) within. But if it is “clean” air, then it will have a few large cloud droplets within it. For the droplet to fall, it needs to grow, as they fall dependent on their size and weight. A droplet will collide and coalescence (the joining or merging of two elements) with other droplets as it is falling through the sky growing in size during its fall. The larger the droplet gets, the faster the fall, and the more it will collide with other droplets. This will create a supersaturated cloud and once it has a lifting mechanism, rain will fall.
 
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© 2019 Weather Forecaster Allison Finch