h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Another question courtesy of PaperKid (now 6)

It was cold this morning, and we could see our breath (though I didn't notice until she pointed it out). Now, I know what causes that, and can actually explain it coherently *strews pillows for those that have endured Amy-explanations, for when they faint with shock*

What I was wondering was this--it was colder yesterday morning, yet we didn't see our breath. It was lightly drizzling, but I don't remember any wind. My hurried, get-in-the-car-or-we'll-be-late explanation was that the rain washed the breath out of the air, and I *know* that's rubbish. Now, did we just not notice, could there have been a breeze, or could there actually be something to my explanation?

surprised not to see the smiley in that post

Well, our breath wasn't *that* visible this morning.

That's my story and I'm sticking to it

I suspect you'll see your breath condense in very dry air.

If the air is 100% humid already - i.e. it's raining - then it's going to be difficult to see water condensing onto water that's already there.

Good question

Isn't vapour more likely to condense in wet air?

Yes but you won't see it will you as it's already precipitating.

Or at least that's my guess - I'm just trying to explain the observation. I don't really know the answer.

My point is that it I think the contrast between dry air and your wet breath is greater and therefore leads to an obvious condensate coming out. In wet weather your breath may well be much closer to equilibrium with the air water content and therefore you perceive nothing.

Or like I told Faith--the rain washed it out

I am going to add my here

If you can 'see your breath' outside, the air temperature must be *very* cold. Near freezing.

When you exhale, your body releases water vapour from your lungs as a result of respiration, by removing carbon dioxide from the blood and the water is part of this process, as a waste product. Exhaled air is actually saturated with water.

Condensation occurs when any of this saturated water finds something cold to condense onto, these can be minute particulates in the air, or other colder water molecules, and a visible water vapour can be seen.

Also, this usually happens when the air is very still, allowing these tiny clouds of fog to linger for a second or two before being dispersed. If it was windy, you don't get to see this happen?

I think that when it is raining, your breath remains invisible, because the air around you is also saturated, and no more condensation would be possible. I also think that the temperature would be higher, when it is raining than when the air is clear and your breath is visible - it may just *feel* colder, or the chill factor may be greater.

I can't test it - but maybe some of our Canadian friend will be able to - does your breath show when it is snowing? It is so long since I have seen snow falling, I can't remember, but I seem to think that this is the case.

Another test for your child would be to look at the breath when in a steam filled bathroom - where the air temperature is warm - you can see visible water vapour, but not your own breath unless you breathe on a cold mirror

It doesn't have to be near freezing to see your breath--I've seen it quite often between 45 and 50 F (7ish to 10 C)--that being, for me, the range of not-worth-going-back-in-for-a-coat-if-I-don't-already-have-one-unless-I'll-be-out-awhile-or-it's-getting-dark-or-raining.

I'll be singing with a meteorologist tomorrow. I could always ask him.

Your breath will be visible even in very windy weather. Many a dark, cold and windy winter's morning have I been watching my breath flow out into the wind while waiting for the bus.

what is sex weather ?

Anything that turns you on

More seriously, I guess you're new so welcome to SEx or Science Explained (hence the SEx).
It's good nettiquette to preface conversation titles with SEx: to alert people who have subscribed here that it is a Science Explaind thread and not from anywhere else in the morass that is h2g2.

So SEx: Weather - is a weather question posted to the SEx forum

Well, Ti, it *does* get just a wee bit chillier where you are I've noticed that the colder it is, the more persistent breath visibility is, which makes sense.