wind chill

[low_delta]

A CNN article about the cold says wind chill is an effect of the wind that makes it feel colder than it really is. That's not exactly the point. The wind actualy cools things faster, so your flesh will actually freeze more quickly than it would if there was no wind. I think saying that it "feels" colder understates the issue.

They're saying the temperatures are low all over the country - from the midwest to Arkansas to Florida to the northeast. But Fairbanks, in central Alaska is in the 20's right now. A friend in San Francisco says it's 75, which is warmer than usual.

There are record lows being posted all over Wisconsin. I'd be surprised if our -13 is a record.

Comments

[mummm.livejournal.com]

Well... it's durned COLD!

[marswalker.livejournal.com]

Wind chill only affects evaporative-cooled things.. like humans, supposedly; but I agree in that the real affect is that moving air of any cold temperature removes heat from any surrounded warm item faster than static air.

[emschin.livejournal.com]

Now this is something I've wondered about for a long time. Your comment explains why they say only animals are affected. But, (and now comes the dumb question) what about cars? If moving air of a cold temp removes heat from any surrounded warm item faster than static air, does your car get colder faster if in the wind?

[marswalker.livejournal.com]

And indeed, yes, cold moving air will remove heat faster from any hot item than the same are not-moving. Which is why we have a big fan blade at the front of the motor... to move the air through the heat exchanger (radiator).

Not a dumb question at all.

The big difference between animals/humans and, say, warm rocks, is that evaporative cooling works on a liquid absorbing heat and evaporating; the wind blowing will make the water evaporate much faster, pulling more heat out of the warm system. Humans use evaporative cooling, where as warm rocks more or less don't evaporate. :)

[low-delta.livejournal.com]

When liquids evaporate from a surface, that surface actually becomes cooler than the surrounding area. The greater the speed of evaporation, the lower the temperature. Notice that alcohol evaporates more quickly than water? And how cold it feels on your skin?

Moving air only speeds the cooling of warm things (like people or houses or cars that have recently been running), so they reach ambient temperature more quickly.

[low-delta.livejournal.com]

How are humans evaporatively cooled?

[marswalker.livejournal.com]

Your body wants the air immediately surrounding your skin to be at about 90% humidity, so it constantly releases tiny amounts of water from your skin (perspiration). For two, when you get hot, your skin produces more perspiration, so it can evaporate and cool you. These are both part of the same mechanism.

Your skin may not /feel/ moist to the touch, but there is a large amount of water in it. Wind - cold or hot - will extract more water from your skin.

So weather you're hot or cold, there is water constantly evaporating from your skin.

[low-delta.livejournal.com]

Oh yeah, sweat. Duh.

[marswalker.livejournal.com]

Here - http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/sweat.html - a more technical discussion of the same...

[raven-nest.livejournal.com]

Had a flister post that it hit 89 somewhere in Cali.. he lives up in the mountains, but I don't know where. Sis says it was 4 last night in northern Arkansas. It has dropped from 52 (our high today apparently) at 11am here.. and we are supposed to hit 12 as a low tomorrow night.

It seems it is colder than normal all over the US EXCEPT California.

[marswalker.livejournal.com]

It's going to hit perhaps 70 today in the desert - from about 38 last night.

[raven-nest.livejournal.com]

Is that warmer than usual for this time of year? That is our "norm" for highs.. but lower than our lows. 65/45 is norm temp with a few cold snaps tossed in... perhaps one or two days a week lower than that for winter.