What kind of clouds are these, please?

Question

The clouds are like white 'cauliflower' type clouds (cumulus??) but they are completely flat at the bottom (which is very dark grey, even black). It almost looks as though they have been cut in half.

Today they completely filled the sky and had the appearance of being stacked on top of/in front of each other. It was a slightly surreal, almost comic-book sight.

So my questions are:

What are the clouds called?

Do they denote any particular weather activity at the time?

Do they foretell any particular weather to come in the near future?

Thanks for any pertinent replies.

Answer 1

I have a question for you: Are you in the US? If so, are you in the eastern part of the US? If so, is the blue sky bluer than usual and your air temperature cooler than normal with comfortable humidity?

If so, I can explain the development of these clouds. These are undoubtedly cumulus clouds, and not necessarily cumulonimbus clouds (CBs, aka thunderstorms). They could potentially become CBs if the upper-level dynamics are such and enough daytime surface heating takes place. Or, they could just become towering cumulus. Or, there could be many smaller ones with an occasional bigger one here or there.

On the eastern half of the US, we're experiencing cooler than normal temps because of the location of the jet stream.  With cooler air at the surface comes overall stability in the atmosphere because of subsidence, or downward vertical motion  (cool air sinks). However, daytime warmth of the sun (we are still in August, after all) provides enough low-level instability to cause lift to form cumulus clouds, and because of the cool air aloft some of these may become storms. The bases of these clouds look so flat because the height at which air particles must lift to condense (the LCL or lifted condensation level) is the same over the region. This height is obviously based off of temperatures and dew points (the lower a dew point, the higher the air particle must rise to cool to meet its dew point). So, the cloud bases probably aren't terribly low, maybe 4,000 or 5,000 feet. They look dark on the bottom most likely because the air is relatively dry and crisp and you don't have a haze reflection bouncing off the bottom of those clouds. You are actually seeing the shadow that the clouds create.

So, basically, what you are experiencing is the summer sunshine effect on cooler than normal temps.

It sure is beautiful to look at, isn't it! I love that weather.

If you are somewhere other than the Eastern US, please let me know because I'd have to do some other analysis. Otherwise, I hope I explained it well. I tried to proofread but I have several distractions here (in the form of kids, lol! Gotta go!

Answer 2

They sound like cumulus-nimbus clouds.  Thunderheads.  They are dark at the bottom cause they are heavy with water.  Means there is a lot of evapotranspiration going on, and it is probably going to rain.  With all the electrostatic build up in those tall clouds it is probably going to be a nasty thunderstorm.

Answer 3

They are cumulonimbus.

that happens because the air surrounding is colder and the vapour condensation line is down from the normal situation, so that the cloud starts to form nearest from the surface and faster than the normal.

Answer 4

http://ww2010.atmos.uiuc.edu/(Gh)/guides...

I think you are talking about nimbostratus, however, the website above should help you decide.

Answer 5

You are correct in thinking they are cumulus! Clouds always have a flat bottom on them, their formation is to do with temperature changes at certain levels, called the dew point, I think.

The fact they are dark at the bottom indicates they are bearing rain and perhaps turning into cumulo-nimbus, or thunder clouds.

If you see a haze underneath them, this is normally rain, if not it could well rain in the near future. There is a wealth of information on weather in books for private pilots etc. A basic book on metrology will give you a lot of information on why, how and where clouds form.