windchill factor question

[sourdough]

when the weather forecaster says it will be minus -25 for example and with the windchil factored in, it will feel like -35 or so,it makes me wonder just how do they know or measure HOW it will feel?
I thought that every person would feel the cold differently depending on how resistant/adapted to cold weather are they.
:confused:

[Nostalgic Pushhead]

I know. Today it was just about 50 degrees out. SUMMER! I go out in shorts & sandals and a t-shirt... and everyone's wearing pants and jackets. Its WARM out people!!!

[rlogan]

Wind chill is just envy.

They don't get to sixty five below zero and they're jealous.

So they put on this add factor to pretend they're howlin' with the big dogs.

Sort of like breast implants.

[nermal]

I've heard weather people say that the temp is so and so, but with windchill, it's 30 F--"so watch for ice on those roads!!":eek: :eek:

Ed

[simian]

Warning! Simplification ahead:

As I understand "wind chill", it is a measure of how fast heat is removed from a person (from exposed skin, if I remember correctly). With no wind and a given temperature, there is a rate of heat loss. Knowing the temperature and wind speed allows the rate of heat loss to be estimated. This heat loss rate can then be related back to what the temperature would need to be with no wind (wind chill).

As for ice on roads: the first place it will usually form is bridges/overpasses/other locations where radiation is the main form of heat exchange. When the temperature drops to about 38ºF (3 or 4ºC), frost can begin forming because the equilibrium temperature for the structure can drop below freezing.

Simian

[Majestyk]

Warning! Simplerification ahead!

Still air has some insulating benefit. Moving air does not.

[nogods4me]

They also play that game here in B'more during the summer. The weathercaster will say something like "The high tomorrow will be 87 and with the humidity at 60% it will feel like 95 degrees" IIRC they call it the "Heat Index"

[Loren Pechtel]

Originally posted by sourdough
when the weather forecaster says it will be minus -25 for example and with the windchil factored in, it will feel like -35 or so,it makes me wonder just how do they know or measure HOW it will feel?
I thought that every person would feel the cold differently depending on how resistant/adapted to cold weather are they.
:confused:

What they are saying is that -25 + that wind will feel the same as -35 and no wind. What that feels like to any given person varies.

[anthrosciguy]

Originally posted by Loren Pechtel
What they are saying is that -25 + that wind will feel the same as -35 and no wind. What that feels like to any given person varies.

Except that the first sentence you give contains the problem of wind chill -- it assumes that all people will feel the same about the effect of a certain amount of wind added to a given temperature. I seem to remember they changed the method of determining wind chill a few (some) years back. I don't remember any details about that though. I do know that the wind chill stated now for where I am feels fairly correct to me, while the wind chill stated a couple decades ago, whenever it was they started using it all the time on forecasts, didn't feel at all right. I don't know whether that's the method used, the area I'm in now versus then, or just me.

[Loren Pechtel]

Originally posted by anthrosciguy
Except that the first sentence you give contains the problem of wind chill -- it assumes that all people will feel the same about the effect of a certain amount of wind added to a given temperature. I seem to remember they changed the method of determining wind chill a few (some) years back. I don't remember any details about that though. I do know that the wind chill stated now for where I am feels fairly correct to me, while the wind chill stated a couple decades ago, whenever it was they started using it all the time on forecasts, didn't feel at all right. I don't know whether that's the method used, the area I'm in now versus then, or just me.

They fixed the formula.

[anthrosciguy]

Originally posted by Loren Pechtel
They fixed the formula.

So there's still limited evidence that I'm not sane. :)

[Silent Acorns]

If anyone is looking for answers to questions about wind chill, you can find them at Environment Canada's Wind Chill page (http://www.msc.ec.gc.ca/education/windchill/index_e.cfm). Also see their Science and Equations page (http://www.msc.ec.gc.ca/education/windchill/science_equations_e.cfm) for some interesting information about how the current equation works and why it is better than the old equation.

[Worldtraveller]

Seems to me taking a poll on how something feels is not a good, or scientific way, of going about determining something like that.
There are however, sound, basic, scientific principles behind both wind chill, and heat index.
The term wind chill comes from a simple comparison of heat loss of an object (i.e. a human body) in still air, radiation and 'bouyant convection' being the main cause of heat loss, as well as the natural moisture in the skin, as opposed to the forced convection that you get when you are standing in wind. You blow on a spoon of hot sop for the same reason, forced convection causes faster cooling.
So the 'temperature' with wind chill is equivalent to what you get in still air at that temperature.
Heat index is similar. Because the body evaporates moisture to cool, in a dry environment (I really miss Arizona) this process is much more efficient, as moisture evaporates more rapidly in dry air. The heat index, again, is a comparison of how effective your body's evaporative cooling is in dry air of a given temperature to the actual temperature given the high humidity. So in humid air, your body's evaporitive cooling doesn't work as well, since evaporation is hindered by the existing moisture in the air.
If you want a more exact, engineering based explanation of these concepts, google for Psychrometric Chart, and you will find several good pages.

Cheers,
Lane, thermodynamicist turned structural engineer.

[Demosthenes]

I know. Today it was just about 50 degrees out. SUMMER! I go out in shorts & sandals and a t-shirt... and everyone's wearing pants and jackets. Its WARM out people!!!

you're crazy, 50 degrees' FREEZING. You can tell that I come from warm climates. Last week we had 70s and now it's low 60s here, not too bad some cool breezes but it's full sun out with no sight of clouds. A mild weather indeed. I can't wait for the mid-80 degrees weather to arrive.

[rlogan]

you're crazy, 50 degrees' FREEZING. You can tell that I come from warm climates. Last week we had 70s and now it's low 60s here, not too bad some cool breezes but it's full sun out with no sight of clouds. A mild weather indeed. I can't wait for the mid-80 degrees weather to arrive.


Haw! Sixty below zero (raw temperature) is freezing.

Forty below is cold.

Ten below is pretty much perfect. The snow doesn't melt on your gloves. I hate that.


At about fifty below you can go outside and throw a glass of water in the air. It will vaporize completely. Nothing hits the ground.

[Worldtraveller]

Gaahhh!!! 50 below?? I think I would shatter in that kinda cold.
But to me, 110 in the shade, with little to no humidity is heaven!! (sorry for the analogy :D)
I rused to ride my bicycle all year in Arizona, and below 70, I would have to bundle up for the first few miles.
And nothing beats 140 miles from TUcson to Phoenix in the middle of august. :cool: I found out I get about 70 miles to the gallon (water/gatorade).

Cheers,
Lane

[Vinnie]

I wrote an article on wind chill (http://www.after-hourz.net/wx/windspeed.html):

How cold you feel outside generally depends on a number of things: sunshine or a lack of it, your metabolism (which means it can fluctuate slightly from person to person), the air temperature, the wind speed, your shelter, amount of bare flesh exposed, humidity and your clothing. The wind chill index measures two important elements: the impact of air motion and air temperature on your bare skin. We shall explain the basics behind windchill and alleviate some common misconceptions below.

It also explains the basics of wind chill and uses the new formula.

I like weather a lot so I started making a weather page:

http://www.after-hourz.net/weather.html

Just don't have a lot of time to write articles, make jokes, engage in debates...yadda yadda...

Vinnie

[anthrosciguy]

Gaahhh!!! 50 below?? I think I would shatter in that kinda cold.
But to me, 110 in the shade, with little to no humidity is heaven!! (sorry for the analogy :D)
I rused to ride my bicycle all year in Arizona, and below 70, I would have to bundle up for the first few miles.
And nothing beats 140 miles from TUcson to Phoenix in the middle of august. :cool: I found out I get about 70 miles to the gallon (water/gatorade).

Cheers,
Lane

When I was a kid in Rochester, Minnesota, in the spring it would get up in the 20s and 30s (F) and we'd be running around with our coats unzipped while visitors to the Mayo Clinic would be bundled up in heavy coats and those Russian style hats.

On the other hand, I was in Vegas one summer for a car race and one fellow there was English and he was suffering bad even though it was only about 95 F -- the guys I was with had raced in the UK and said the locals there would start passing out in the cars at times when it got above 70F (mind you, in racing cars you're wearing long fireproof underwear and a quilted racing suit). Our guy was Armenian and he'd get out of the car hardly sweating.

[rlogan]

Gaahhh!!! 50 below?? I think I would shatter in that kinda cold.
But to me, 110 in the shade, with little to no humidity is heaven!! (sorry for the analogy :D)
I rused to ride my bicycle all year in Arizona, and below 70, I would have to bundle up for the first few miles.
And nothing beats 140 miles from TUcson to Phoenix in the middle of august. :cool: I found out I get about 70 miles to the gallon (water/gatorade).

Cheers,
Lane



At thirty below zero, 16,200 ft. up on Mt. McKinley I put ice screws into a wall and tried to put my radio antenna over the ridge to radio a camp down at 14,200. The weather service the next day said the winds were gusting to over 100 mph. I saw shards of ice bigger than me being blown up the wall and rocketing off into space.

The guys next to us had not dug their camp deep enough and the wind literally blew them off the mountain. Picked the three of them inside their tent up and blew 'em away. We did find them, in their underwear, on a tiny ledge with about a ten thousand foot drop off the west buttress to the glacier below.

We put the rescue on 'em, but they lost fingers and toes. I could not hear the people I was trying to radio, but they heard me. They got a chopper up the next day to us. The chopper couldn't land. He hovered over the abyss so the guys could be stuffed inside.

You just can't buy entertainment like that. What's the wind chill at -30 F and 100 mph winds? Not sure, but you really know you're alive when you're in the teeth of it.

[Worldtraveller]

Ok, I had to go soak in a sauna for 60 minutes after reading that...I'm better now.

Cheers,
Lane

[Mr_Stratovarius]

it has to do with the wet and dry bulb temp of the air, moisture in the air sticks to your body cause its warmer and can hold more moisture and because the atoms in liquids are closer than in gasses this film of moisture takes on the cold air faster. Plus the wind takes away the film of warm air that insulates your body. Heat loss theory from buildings apllied to humans haha. :D

[Valdemar]

it has to do with the wet and dry bulb temp of the air, moisture in the air sticks to your body cause its warmer and can hold more moisture and because the atoms in liquids are closer than in gasses this film of moisture takes on the cold air faster. Plus the wind takes away the film of warm air that insulates your body. Heat loss theory from buildings apllied to humans haha. :D

My dad likes to call it "Yuppy Temperature" here in Minnesota.

Wet bulb temperature, if I remember from physics, is when you take a thermometer, wrap it in a wet cloth, tie a string to it and swing it around in the air. You can cool the thermometer to below ambient temperature due to the evaporative effect of cooling.

People at my work like to argue that their cars feel the effects of wind chill!! Just think, we've got yuppy cars here in Minnesota!

Seriously, though, I simply tell them that the cars cool faster in the moving air mass than if the wind weren't blowing. The energetic molecules are whisked away by the moving air. Of course, you could cool the engine below ambient temperature by hosing it down on a windy day.

[mrmoderate]

The wind chill factor is the calculated evaporation of the moisture on human skin based on the ambient temperature of the air in conjunction with the rate of speed of the wind.

As air travels across moisture, the moisture evaporates. The process of evaporation absorbs heat from the body which makes you feel colder than the ambient temperature. This is why we fan ourselves in the summer.

Furry animals do not feel the wind chill except on their noses and mouth where they have all of their bodily moisture release. Humans have sweat glands all over so we can feel the wind chill factor more.

Since the wind chill is actually removing heat from our bodies it is an actual viable condition that should be paid attention to. Your body is going to lose more heat faster in windy conditions at the same ambient temperature than without the wind.

The wind chill factor as far as the formula and the wind chill charts have been altered over the years as we understand it's cause and effect better.

Wind chill alone will not cause freezing conditions. Wind blowing over a dry 33º road will not drop the temperature of the road. If you add water to the road, the evaporation process of the water due to the wind factor will absorb heat from the road and lower the temperature.

[Mr_Stratovarius]

as for cars and cold temp, it got so cold for a week here last winter the rear doors on my car wouldnt shut properly it was -20'f, brrr time to move to the tropics