Friday, February 05, 2010

Not so simple.

It's still snow here and tonight the light rain has turned the street into a skating rink. I'm not driving on that. There are signs of melting so maybe, soon, life can get back to normal.

So I've been browsing and I keep coming up against the question 'can it be too cold to snow?'

The obvious answer is - if it could, there'd be no snow in the Arctic or the Antarctic. So it can't. And yet the pseudoeducated keep coming up with 'Yes it can'. Their argument is that at sub-zero temperatures, the air cannot hold enough moisture to produce any precipitation.

*sigh*

It's partly true, and that's why it rains/snows. The argument requires a static system and we don't have one. Air moves about. The technical term for this is 'wind'. In warmer regions, air picks up moisture. When moisture-laden air moves into colder regions, the moisture drops out. Depending on the temperature of the colder region, it could drop out as clouds, rain, snow or hail. Warm and cold are relative terms so the moisture content of air at zero degrees will drop out if the air cools to negative degrees. All that matters is the difference in temperature, not the absolute temperature itself.

So the argument that cold air can't hold moisture is not a justification of the 'too cold to snow' myth. It's an explanation of why snow (and rain) happens at all. Warm wet air comes into a colder region and the moisture it contains precipitates. That's how come it can snow in Antarctica at temperatures in double figures below zero.

It cannot be too cold to snow. It all depends on whether incoming air was warmer before it arrived.

The other thing I found was centrifugal force, which I was told at school was a myth.

Perhaps not.

2 comments:

Southern Writer said...

Hmm. Well. I'm no scientist, but I did live in the Rocky Mountains of Colorado for 20 years where it snows 9 months out of the year. I've seen it snow on the 4th of July twice (and we're talking the northern hemisphere, not the southern). I'm not saying that it can't snow if the temperature drops to a certain point, but I can say it rarely did. If the temperature fell much below 30 degrees Fahrenheit, as a general rule, it did not snow.ba

Romulus Crowe said...

SW- you lived where it snowed that much? It would drive me insane!

Depends on the terrain. If there's no source of warmer air coming in, then the cold can't make it lose its water. So the 'too cold to snow' can be both true and not true, depending on individual conditions.

It can't work in the UK because we're a little island surrounded by water. Often described as 'the rainy islands at the edge of Europe'.

Something drops out of the sky most days here. I haven't seen a dry patch of ground for months.

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