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Flightinfo's sexiest user
Dec 21, 2001
Hey guys,

Got a quick question about clouds.

On my way home, I noticed how one half of the sky was completely OVC, while the other side was SKC. How can this be? How can the skies be clear to the West, and OVC to the East (or North, South, etc)?

It just seems a little odd. Maybe there is sinking air in these regions, in order to replace the updrafts from the rising air? Or does it have something to do with the wind?

Also, when there are patches of cumulus or other type clouds, how come there are spaces in between them? How can only a small area be saturated beyond the downpoint?

Any replies greatly appreciated!


What do you call a body of air that has uniform properties of temperature and humidity? What do you call the place where those two bodies meet?

When a warm moist airmass meets a cooler airmass, what happens? You probably know the answers to these questions; think about them, and you've answered your own questions.

As for cumulous clouds not being continuous, this is typically the result of either convection or wind. An airmass which is disturbed by convective activity may have warm, moist air rising up through the mass, which then condenses and becomes a cumulous cloud. If it continues to build and develops a cycle, it may become a cumulonimbus cloud, raining, producing high winds, rain, hail, the works. It feeds itself.

Lifting action may be convective, such as heating from below. It may be mechanical or orographic in nature, such as moist air being pushed upslope by the movement of the airmass. It may be frontal. The bottom line is that as the air is lifted, it cools, condenses, and clouds form.

A frontal meeting is little different. A common formation is a cold front, pushing warm air ahead of it aloft, where it cools and forms clouds, and various types of weather. In the case of a cold front, this happens quickly, with the slope of the two airmasses being short in distance. A warm front works just the opposite, and generally you don't see the clearly defined separation between the two airmasses manifest as a line of clouds. It's often more subtle, with high clouds preceeding the actual front by hundreds of miles in some cases. Clouds tend to generally descend as the front approaches, until the actual frontal weather arrives, and passage is marked by a shift in wind.

You're doing the right thing. Study weather every moment you see it. It's vitally important to flying, and in fact, to daily life. There are many notable books out there on the subject, such as Weather Flying, by Bob Buck. However, I'd start with Aviation Weather, published by the FAA as AC 00-6A. You'll find that as you read, you will begin to see evidence of the subjects you study, in the sky above you, and then it begins to take on real significance. Good luck!!
Hey avbug,

Thanks for that response.

I asked this question to others too and it seemed that they all believed it was a front where two different air masses met, as you alluded too. However, after a few hours or so, the sky cleared. If the front was advancing, shoudn't the SKC area have become OVC, or at least have some significant cloud cover?

You're right about studying the wx. This is my favourtite subject from groundschool, and I think the most interesting.

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