 Poster: A snowHead
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DB, Temperature is NOT expressed as 'wind chill'. Wind chill is a very specific term which relates to a perception of temperature. Any other description and you are not talking about wind chill anymore.
Just look it up... it's simple.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Did you go through mist or fog on the way up? The moisture could freeze to the bottom of your skis.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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volfy, no, just snow. Though that may still have been the cause, I suppose.
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You need to Login to know who's really who.
You need to Login to know who's really who.
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| bar shaker wrote: |
| James the Last, You miss the point. |
With the greatest of due respect, I don't think that 'Wind Chill Factor as experienced by humans' is the point. The point is the effect of wind when chilling a body warmer than the ambient temperature.
I think we agree that:
1. A dry body - animate or inanimate - will cool to the ambient temperature. If there is a wind, then this cooling process will be faster.
2. A wet body will chill to a temperature below ambient.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| Scarpa wrote: |
DB, Temperature is NOT expressed as 'wind chill'. Wind chill is a very specific term which relates to a perception of temperature. Any other description and you are not talking about wind chill anymore.
Just look it up... it's simple. |
There's such a thing as wind chill temperature (just look it up ..... it's simple)
http://www.webmath.com/windchill.html
http://www.nws.noaa.gov/om/windchill/
Yes it's normally used to determine the danger for humans from cold weather (Frostbite etc). Wind chill is felt by humans because of the increased heat transfer. A wet pair of skis won't feel it but will also experience an increased rate of heat transfer. Quicker cooling of the water on the skis = iced up skis.
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You'll need to Register first of course.
You'll need to Register first of course.
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James the Last,
What about a pair of wet skis?
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| DB wrote: |
| bar shaker wrote: |
| I agree with Scarpa. Windchill is a 'feels like' effect as the wind will take more heat from a warm object that it would otherwise lose in still air. |
So if the person was dead it wouldn't be wind chill? |
Correct, now you are getting it.
| DB wrote: |
| This causes the water to freeze at a much quicker rate than it normally would |
My word, he has it.
| DB wrote: |
| that temperature is expressed as the wind chill temperature. |
Oh, maybe not.
Bar Shaker has it:- The skis cool to the ambient air temp, irrespective of if that air is still or it is blowing at 30mph. Wind will make the skis cool to the ambient level more quickly but once cooled, that's it, no more cooling.
The human body is constantly generating heat and we radiate this heat at rates depending on our insulation from clothing and any air stream we are exposed to. If our skin is exposed to a strong cold air stream, we radiate that heat more quickly and this constant draw of heat from us at a high flow rate feels like we are exposed to a colder temperature than the air temp really is. Our nervous system can sense this accelerated flow rate and we feel that the air must be colder than it really is. This feeling is called the Wind Chill Factor.
There is a formula to provide a guide to the feel of wind chill but you can't actually measure it although there is a company that makes a meter which combines wind speed, temperature and the formula to give an indication. It feels different to different people. Take a look here for a reasonable explanation. http://www.slate.com/articles/news_and_politics/explainer/2005/01/how_they_measure_wind_chill.html or http://en.wikipedia.org/wiki/Wind_chill or http://www.icebike.org/Articles/windchill.htm
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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| DB wrote: |
| Wind chill doesn't only affect human beings, hence the reson people blow on soup to cool it down. The wind causes more water to evaporate off and this increases cooling of the ski surface = water freezes up quicker. As others have said, it sounds like the ski has come into contact with water (either on the ground or freezing fog) and then frozen on the way up. |
| Quote: |
| For inanimate objects, the effect of wind chill is to reduce any warmer objects to the ambient temperature more quickly. It cannot, however, reduce the temperature of these objects below the ambient temperature, no matter how great the wind velocity |
http://en.wikipedia.org/wiki/Wind_chill
My statement was that wind chill does affect and is also applicable to inanimate objects.
Yes the wind cannot cool the object below ambient if the object is dry but evaporative cooling can cool below ambient temp.
Are you sure the body radiates more heat in increased wind or that heat loss is increased through accelerated convection and through increased evaporation from the skin (latent heat of evaporation)?
A lot of this is semantics and straw man arguments. In simple terms when there's a wind and the skis are wet then the water on the skis will freeze up quicker in sub zero temps, whether it's to ambient temperature or below ambient temperature is irrelevant if the ambient temp is -7 Deg C (at atmospheric pressure).
I'll leave this now and get my touring kit packed for tomorrow's ski tour.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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DB,
An inanimate object will be cooled to the ambient temp and then stops cooling. If that inanimate object is wet, evaporation cooling may temporarily cool it to below ambient temp but once the water is frozen and the evaporation stops, the cold wind would quickly raise the temperature to ambient. 'Wind Warming' ?
You are correct that the heat lost by a person is convective, I was trying to be simplistic.
My point remains, Wind Chill describes the temperature that the person feels like it is, based on their rate of heat loss. The temperature shown on a thermometer bulb will be the same, irrespective of varying wind speeds and any calculated Wind Chill Factor.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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Yes
I've had weird things happen to skis and its not purely tmeperature driven , it seems a combo of humidity and temp.
I'm in the wind chill doesn't affect inanimate obejcts camp.
Sometimes the snow is sticky here; its usally temp, but also a combo I think of humidty, temp and snow temp. Cold weather waxes can prevent this.
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| saikee wrote: |
You guys must pretty high up in the food chain of skiing.
I have never come across a run with a river in it. The only time I got my ski wet was when the snow melted into a pond of water in the middle of a run. |
I've done loads of off piste runs which involve crossing a stream (usually with skis off, stepping from rock to rock).
On that occasion we were skiing beside a small river (returning to St Anton from the back of Stuben) and the guide said "keep your speed up at the turn" and then turned across the river onto what I assumed was a tiny bridge but realised as I was about to go on it was just a snow-covered tree trunk about 9 or 10 yards long and just barely wide enough for two skis. The first person following the guide got across and I got most of the way and then fell off, landing just on the bank with one ski in the water. The third person was so scared he slowed and only got half way across before stopping (I think he managed to slowly shuffle the rest of the way). "It is good that you have a good sense of humour" said the guide. A bit further on we passed a proper bridge. HO ho!
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You know it makes sense.
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It's happened to me before as SpyderJon said it's down to a lack of wax on your skis - He should know, since he owns a Piste Office
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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| saikee wrote: |
| I have never come across a run with a river in it. |
In Canada they call them "creeks" - early season you'll have exposed creeks at lower altitudes, more or less depending on the way the weather's worked that season. This year there were a lot of exposed creeks in December.
You will find a one to three meter drop into a creek here and there; it's just something else you need to keep your eyes open for. Obviously on piste they're going to be marked, and most pistes are designed to avoid them. You can find some in-bounds here and there though.
I once saw someone fall off a chairlift into a creek - I think that was Lake Louise I think. Otherwise I once helped rescue a woman from a creek in the back country. When it's cold, your time in that state is limited. We had her heli-ed out of there within minutes, but it felt very scary.
So yeah, get out more, you'll find rivers enough..
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Poster: A snowHead
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I once saved a girl from drowning when skiing off-piste. It was on the Lac du Lou, up the valley from Les Menuires, below Val Thorens. We were skiing across it and there was one obvious small patch near the run-off that wasn't frozen and a girl in our party made a mistake and fell half in. She was holding onto the edge of the ice - one arm and one leg under the ice and on arm and one leg on top with skis still on. I pulled her out. The guide hadn't noticed!!! Luckily we weren't far from a chair lift home to Val Thorens but she was very cold on that lift!
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| bar shaker wrote: |
DB,
An inanimate object will be cooled to the ambient temp and then stops cooling. If that inanimate object is wet, evaporation cooling may temporarily cool it to below ambient temp but once the water is frozen and the evaporation stops, the cold wind would quickly raise the temperature to ambient. 'Wind Warming' ? |
Yes but if the skis are wet the evaporative colling will be much greater than from a human body, the skis can't feel the cold but the rate of cooling will be much greater. e.g. If a person was wet the real wind chill temperature would be much lower.
| bar shaker wrote: |
| My point remains, Wind Chill describes the temperature that the person feels like it is, based on their rate of heat loss. The temperature shown on a thermometer bulb will be the same, irrespective of varying wind speeds and any calculated Wind Chill Factor. |
A person asked why their skis frooze up so quickly not what Wind chill temperature was. I said wind chill affects inanimate objects i.e. the wind causes an increased rate of cooling especially if the object is wet = the skis cool very quickly and freeze up. The rate of cooling from wet skis in the wind at an ambient temp of -7 Deg C could be equivalent to the skis suddenly being exposed to sub -20 Deg C temps or much lower. The same happens if you spray water onto a moving car's windscreen in cold temps - it suddenly freezes up.
Are you saying the wind doesn't increase cooling on a wet inanimate object?
Wind also increases heat loss from exposed buildings, hence the reason Building Services design Engineers increase the Heating requirements for such buildings. The wind chills/cools the building more as the convection heat loses are greater.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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This has been my theory on the phenomenon after first experiencing this puzzling effect a few years ago - This effect can happen on chairlifts that have a moving "segmented" belt at start point and when at certain temperatures water is present on the belt, it adheres to ski bases and freezes on the way up (as temperature decreases with increasing altitude and the water is assisted in freezing with evaporation). Probably more likely to happen with skis that have not been recently waxed. Only action is to scrape ice off at top station (use one ski to scrape the other), then to get skis waxed or avoid the offending chairlift/weather condition. I have seen this effect happening now and again on the "Gron" Chairlift in Les Carroz, start altitude about 1400m, finishing about 1800m.
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You need to Login to know who's really who.
You need to Login to know who's really who.
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skier52, interesting theory. I do recall a moving carpet thingy, so you might be on to something. We used the scraping technique you mentioned but didn't realise the wax might be an issue. If it happens again, I'll put the skis in for an overnight waxing.
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