Thunderclouds like the ones you've been seeing on the horizon in recent weeks typically have short lifespans. Gary Robbins

We recently asked National Weather Service forecaster Alex Tardy to explain why San Diego, Riverside and San Bernardino counties have had so many thunderstorms in recent weeks. (Turns out it is a seasonal thing, mostly.) We chatted Tardy up again when we became curious about the life cycle of a thunderstorm. Here's some of the bullet points he provided, based on the type of photographs we've been publishing.

Q: How long does it take for a thundercloud to form and fall apart?

A: Usually a one hour cycle, from cumulus to cumulonimbus (thunderstorm). Individual storms can last longer in the right environment (wind shear, boundaries, high instability).

Q: Is there a big difference in wind speed -- and wind direction -- at various altitudes in the clouds?

A: Wind speed is light through the height of the cloud (its growing straight up). Temps are likely in the 20s at about 18,000 feet in the storm ... The strong storms we have been seeing of late (lots of lightning and heavy rain) are upwards of minus 40 degrees at the top.

Q: Why are there cotton ball-shaped areas in thunderclouds?

A: Those are the turbulent areas of the cloud -- rising air which condenses into cloud droplets as it rises and enters cooler air.

Q: Some areas of these clouds are gray. Why?

A: They are likely lower, younger (newer) clouds that are in the shadow of the tall thundercloud (so there is no sun on them.) The sun angle appears rather low (in the late afternoon) and the side of the storm is showing up bright (higher portions).

Q: Does the entire cloud move in the same direction? How fast do clouds like this move?

A: Usually the answer is no for a mature thunderstorm. But in this developing cumulus (towering cumulus or young thunderstorm) the cloud mass is likely mostly moving in the same direction except, possibly, the lowest clouds or the bottom of the storm (if you were underneath).