Re: How fast does rain, hail, and fog strike the ground?

The terminal velocity of hydrometeors is a function of their diameter. Fog droplets are little more than large cloud droplets, with a diameter around .02 mm. Raindrops are generally defined as having diameters of between .2 and 6 mm. Average raindrops are about 2 mm in diameter. Drops larger than 5 mm generally break up into smaller drops before reaching the ground. Drops of 2 mm in diameter have a terminal velocity of around 6.5 cm/sec. The spectrum of diameters from .2 to 6mm would have terminal velocities from 2 - 9 cm/sec.

Fog droplets don't really strike the ground...if they did, they'd be drizzle drops instead. Fog is really just a cloud in touch with the ground. Cloud droplets have a terminal velocity of something like .02 cm/sec. The slightest turbulence or movement of air in the cloud will counteract the gravitational force. In reality...they just float in the air.

Hail on the other hand can strike the ground at ferocious speeds...not all of which is solely attibuted to the terminal velocity of the stones. Hail size and composition range from soft graupel less than 1/4 inch in diameter...to irregular conglomerates of stones 3 inches in diameter or greater. A 3 inch stone has a terminal velocity somewhere near 90 mph. Add to this the fact the hail often reaches the ground aided by the downdraft in the parent thunderstorm. In these instances, even small stones can have very high fall speeds. I had the unfortunate experience of losing a roof and the paint on my car to a hailstorm composed of stones all less than 1/4 inch. Driven by thunderstorm winds of 65 mph, even these small stones were capable of some serious damage. By the way, a thunderstorm is considered severe by the National Weather Service when it produces hail 3/4 inch in diameter or greater, and/or winds of 58 mph or greater.