Can a cloud weigh as much as a 747?

A problem with http://www.straightdope.com/classics/a980313a.html

Clouds are liquid water, not water vapor (not H2O gas.) Ask yourself why liquid helium is so heavy, while the helium vapor rises like a balloon.

A population of tiny water droplets should NOT be bouyant. It should act like a dense fluid, and indeed it does act this way if you use an ultrasonic nebulizer to make some water-mist. Individually the droplets settle very slowly, but the mist itself is far denser than the air, and it can easily be poured from a pitcher into a coffee mug. The liquid droplets weigh the mist down, making it behave like an extremely dense gas.

So why do clouds stay up there? Why don’t they hug the ground like fog does? Simple. Clouds are hot. Condensing water releases thermal energy. If something should push air upwards, the pressure and temperature falls, and at some temperature the water starts condensing onto any handy nuclei. We end up with warm, heavy water droplets surrounded by bouyant hot air, the air being warmed by the droplets.

Be aware that thunderstorms and hurricanes are driven by an “engine” in the form of updrafts caused by air which is heated by condensing water. It’s like a “drafting” effect in a fireplace chimney, where an updraft sucks more moist air into the bottom of the column, and as droplets condense, the air gets hot and rises. It’s quite a bit like a forest fire, but the “fuel” is moist air, and the “combustion products” are hot air and raindrops. Hurricanes are quite a bit like a firestorm, like a pattern where heated air rushes horizontally radially inwards to a central updraft column. I think there’s an added effect where the heavy raindrops pull loose from the hot air, greatly reducing the average mass per volume and leaving the hot air to rise violently upwards. I.e. the “747” made of water is cut loose from the “hot air balloon” which was keeping it aloft, resulting in tons of water falling as rain and a thunderstorm updraft moving at hundreds of km/h and punching upwards through miles of stratosphere.

(IIRC I got this stuff from C. Bohren’s “Clouds in a Glass of Beer.” I’m astounded that SciAm ‘ask an expert’ gets this wrong, and the answer is provided by a meteorologist. But Bohren is an actual atmosphere physicist, so that probably makes a difference.)