By Andi Anderson
April is one of the wettest months in Illinois and across the Midwest, with an average of 4.24 inches of rain. These showers vary from light drizzles to heavy rainfall, and the science behind how raindrops form is fascinating.
Raindrops begin as water vapor in clouds. This vapor clings to small particles like dust or smoke and eventually forms tiny droplets or ice crystals. Even during summer, raindrops often begin as snowflakes or ice. As these crystals move around inside clouds, they collide and grow, eventually becoming large enough to fall as rain.
When a droplet reaches about .008 inches, it starts to fall. As it drops, it keeps collecting moisture, growing even more.
Although cartoons show raindrops as teardrop-shaped, real raindrops look more like tiny flying saucers—rounded at the top with flat bottoms due to air resistance. Bigger drops may have a more curved base.
Raindrops don’t grow endlessly. If they get too big, they break apart. Most raindrops stay smaller than a quarter inch. Their fall speed depends on size and turbulence. Small drops fall slowly, around 6 feet per second, while larger ones can reach 90 feet per second.
In storms, raindrops influence weather. Smaller drops evaporate quickly, cooling the air and causing strong downdrafts, which can lead to damaging winds. But these downdrafts can also disrupt the storm’s energy flow, weakening it. NASA is studying how drop size affects tornado development and storm strength.
Although raindrop size hasn’t changed much, rainfall intensity has increased over the last 40 years. Events with 2 inches or more of rain are becoming more common, especially in the Midwest. Understanding raindrops helps us better predict and prepare for severe weather.
Photo Credit: istock-dusanpetkovic
Categories: Illinois, Weather