Dear Tom,

The largest raindrops in a thunderstorm usually fall at the very beginning of the rain. They are followed by smaller drops that mix in as the rain continues. Why is that? Tommy Korren, Plainfield

Dear Tommy,

It has to do with the raindrop fall speed. Large raindrops fall faster than smaller drops, so a thunderstorm’s largest raindrops make the descent from the storm’s rain production area to the ground more quickly than smaller drops. Thunderstorms usually move at 25 to 35 mph. As the rain-producing portion of a storm moves overhead, big drops arrive first because they are falling the fastest. Fall speed for large drops, diameter 0.2 inches, is about 20 mph, but medium-sized drops descend at 14 mph. Large drops fall 5,000 feet in 2.8 minutes; medium-sized drops in 4.1 minutes.