Another factor beyond humidity and CAPE is a lifting mechanism -- something to get the air moving upwards to start the convection. Fronts, convergence, or low pressure systems can act to lift the air (cold fronts especially force air upwards rapidly). But some of the most powerful storms in the US plains states occur when the lower atmosphere is extremely humid, but capped under a stable layer of warmer air. This is like putting a lid on a pressure cooker, building up lots of energy as daylight heats the surface, and eventually, if the capping inversion is broken, the convection starts vigorously. Violent supercell storms can pop up in literally minutes.

There a way to get water to form droplets without condensation nuclei, but it doesn't usually happen in atmospheres. You can observe it every time you open a soda or beer bottle, as the sudden fog that appears at the top. (I love this article, by the way.) The sudden expansion of the air cools it very severely (well below freezing!) and allows the water molecules to stick together and form droplets. The interesting thing about this is that all the droplets are basically identical -- the same size. This is "homogeneous nucleation". A very different kind of cloud than what we see in the sky.

It probably can't without intelligent intervention, I mean can it be done with intervention somehow?

Would an airliner climbing out from take off or descending towards landing at a big airport contribute at all to breaking inversion caps? It makes me wonder if a Boeing 747 taking off from Denver would cause tornadoes in Nebraska from this kind of butterfly effect.

Reminds me of when I bring ice cold drinks when I go to work at Burger King. Minnesota gets pretty humid in the summer and on hot and humid days, my whole entire water bottle would be shedding fog even when closed, since the employee lounge is next to the kitchen, where it gets *very* warm. Pretty cool.

I reached for a soda in the minibar to cool me down. I put the cool can on the table and it was steaming heavily, forming its own little cloud around itself.

It'd be very hard for a terra with an atmosphere to have no CCNs at all.

What makes you think that aliens would use radio? They may use something completely different that we are missing in our searches for life. Maybe they evolved past a physical state? And are invisible to us with no proof of their existence?

Nothing makes me think that. But We know of no hypercom, so we can not look for hypercom signals. We have to look for normal radio signals.

But who knows? When near the star a ship in the warp goes, or comes out of warp, perhaps we could receive a signal thereof. For example, gravitational waves.

Maybe the reason nobody has responded is because they don't communicate on the frequency we use? Or they don't know of it for some reason.

I think it is not possible. There are just too many ways to produce CCN, and they have such low terminal velocities that the atmosphere would have to be absolutely free of wind and convection for them to fall out. To give an idea, the typical terminal velocity of a cloud droplet is on the order of centimeters per second, which is easily overcome by thermals.

For a cloud condensation nucleus, it's on the order of micrometers per second, or centimeters per day. So if there's any mechanism to generate them, they'll go everywhere. Even in the extremely clear air of the Antarctic, there's enough of them around to generate clouds.

I guess the one sure-fire way to remove a planet of its CCN would be to freeze or blow off its atmosphere entirely.

many would argue that it would be wise to keep radio silence.

What about the atmosphere being wiped of water vapor instead, would enough to make clouds be able to get into the atmosphere before the lakes and seas become groundwater, even if the larger bodies of water weren't all that large?