Wind chill -- How is it actually measured?

[zuz]

How do they measure wind chill factor?

 

[jedishrfu]

Its shown here:

https://sciencing.com/calculate-wind-chill-factor-5981683.html

and this video:

 

[jim hardy]

How do they measure wind chill factor?

I hate that "Wind Chill" hype.
It doesn't feel like the temperature is any lower,
it feels like temperature is what temperature is and the wind is blowing..

 

[DrClaude]

I hate that "Wind Chill" hype.
It doesn't feel like the temperature is any lower,
it feels like temperature is what temperature is and the wind is blowing..

Hear hear!

And even worse than the wind chill is the humidity factor.

 

[russ_watters]

I hate that "Wind Chill" hype.
It doesn't feel like the temperature is any lower,
it feels like temperature is what temperature is and the wind is blowing..

It's even worse when in the news they seamlessly mix or jump back and forth between the real temperature and wind chill.

 

[johnbbahm]

Since how something feels is very subjective, I would hope the formula is based on empirical data.
For me a type of real measurement would be the time difference between
a bowl of water at say -5 C without air movement to freeze solid vs the time with a 10 knot wind.
The moving air would cause quicker heat loss and a faster freeze time.
You would then need to then see what still air temperature correlated to the freeze time of the moving air test.

 

[zuz]

Please correct me if I'm wrong, but I thought wind chill is a measurement of how cold it feels. A bowl of water does not feel anything

 

[jedishrfu]

I viewed the wind chill as something pretty cool (jk). It told me when I needed to really bundle up.

I grew up in upstate New York and knew something of the coldness of winter while waiting for the bus each day. Such a cruel thing for children to endure especially with all that snow that needs to be spherical and launched in such a precise manner so as to hit its target. I remember definitely hitting the wrong target when my ball of icy coldness sailed through an open school bus window landing in the lap of he who shall not be named. (some embellished alliteration here for the PF community -- ie I can't remember who it hit as I ran home as fast as I could)

However, I now know the power of the wind here in Texas especially when walking the dog at night. Its especially nice bundled up with my Notre Dame Football jacket on making me feel like an astronaut on the moon but my legs still shivering from the wind's relentless attempt to remove my thermodynamically generated warmth.

 

[Astronuc]

'Wind chill' is about forced convective heat transfer, which is more effective as wind speed increases.

 

[jim hardy]

And even worse than the wind chill is the humidity factor.

I completely agree.
Having spent winters in in Florida, Idaho, Quebec , and central US,
my testimony is +50F in ever-soggy Florida is more bone chilling than +15F in bone-dry Idaho.
Specific heat of air is 0.24 BTU/lb, for water vapor it's twice that.

 

[johnbbahm]

Please correct me if I'm wrong, but I thought wind chill is a measurement of how cold it feels. A bowl of water does not feel anything

I think of wind chill as how quickly heat is removed from an object, the object can be ether a person or a bowl of water.
The persons perspective is subjective, the bowl of water freezing solid is not.

 

[gleem]

The current wind chill index was determined by using human volunteers. They exercised on treadmills for 90 minutes while having their face temperature, their internal cheek temperature, and core temperature monitored. The heat transfer from and within their bodies allowed the experimenters to determine the cooling rate due to the changing wind speed. From "Understanding Weather and Climate" by Aguado and Burt.

Temperature perception is highly variable both among individuals and within an individual and may not accurately represent the rate of heat loss. Keep in mind while wind chill and heat indices are related to comfort their usefulness is for predicting physical harm that could result.under extreme conditions.

 

[DaveC426913]

I hate that "Wind Chill" hype.
It doesn't feel like the temperature is any lower,
it feels like temperature is what temperature is and the wind is blowing..

It's even worse when in the news they seamlessly mix or jump back and forth between the real temperature and wind chill.

Frankly, I think y'all are missing the point.

Wind chill factor and humidex are not comfort issues; they are health and safety indexes.

If a thermometer reads 35 degrees Fahrenheit outside and the wind is blowing at 25 miles per hour (mph), the windchill factor causes it to feel like it is 8 degrees F. In other words, your body loses heat as though it is 8 degrees outside.

That single number indicates how to dress, how long to be out, and how soon to seek shelter so as not to suffer from hypothermia, frostbite, etc.

Likewise, with humidex. At 86F with a 60% humidity, you will overheat as quickly as if the temp is 100. That single number indicates how to dress, how long to stay out and how much effort to exert so as not to suffer from heat stroke.

The weather peeps aren't trying to tell you whether you'll be comfortable, they're trying to keep you out of the hospital due to exposure.

 

[russ_watters]

Frankly, I think y'all are missing the point.

Wind chill factor and humidex are not comfort issues; they are health and safety indexes.

If a thermometer reads 35 degrees Fahrenheit outside and the wind is blowing at 25 miles per hour (mph), the windchill factor causes it to feel like it is 8 degrees F. In other words, your 98-degree body loses heat as though it is 8 degrees outside.

The WCF tells you how to dress and how to behave so as not to suffer from hypothermia, frostbite, etc.

Your example was poorly selected for your point: there is no frostbite risk in an 8F windchill if it is 35F outside. Even when it is below freezing, wind chill is not well tied to frostbite risk. Worse, while for a given person the risk of both goes up with lower wind chill, for a person with more body fat the frostbite risk is increased while the hypothermia risk is lowered.

More broadly, since windchill is calculated for exposed skin, walking into the wind, it can be defeated by ducking and is not valid for adjusting for heat loss through quality insulated clothing, for which wind is largely irrelevant.

And none of these issues of the science have anything to do with the additional issue of news hype.

 

[gmax137]

When I lived in Florida, freezing friends (up north) would ask about the temperature.

I would tell them "90 degrees... oh, that's with the windchill."

 

[jim hardy]

And none of these issues of the science have anything to do with the additional issue of news hype.

That's what aggravates me - the faux import and concern in the delivery ,
They've already told me it's cold and the wind is blowing. I already know from motorcycle days that "cold plus wind equals damn cold."

I know reporting the weather is usually mundane - and what's wrong with calm ?
We need more calm-speak when a hurricane is approaching. Instead they feed hysteria.
.
Thanks Russ...

 

[gmax137]

If a thermometer reads 35 degrees Fahrenheit outside and the wind is blowing at 25 miles per hour (mph), the windchill factor causes it to feel like it is 8 degrees F. In other words, your body loses heat as though it is 8 degrees outside.

Well, up until your body (or the bowl of water in another post) is chilled to 35 degrees. The 25 mph wind won't cool anything down below the actual temperature. Wind chill numbers are about rate of cooling, not final temperature*.

*That might not be exactly correct for skin if you are perspiring. But I don't think that's the case in these "minus 55F windchill" conditions.

 

[zuz]

As far as comfort is goes. I live in Buffalo NY and I would rather work outside when it's 20F and snowing as opposed to 40F and raining.

 

[DaveC426913]

Your example was poorly selected for your point: there is no frostbite risk in an 8F windchill if it is 35F outside. Even when it is below freezing, wind chill is not well tied to frostbite risk.

I pulled those numbers from Google. Pretty sure I didn't suggest they were an example of frostbite risk in particular. I think you know that exposure and hypothermia can occur in a wide range of temps.

Worse, while for a given person the risk of both goes up with lower wind chill, for a person with more body fat the frostbite risk is increased while the hypothermia risk is lowered.

More broadly, since windchill is calculated for exposed skin, walking into the wind, it can be defeated by ducking and is not valid for adjusting for heat loss through quality insulated clothing, for which wind is largely irrelevant.

It's easy to pick apart an imperfect system so long as you don't have to offer a better one.

And none of these issues of the science have anything to do with the additional issue of news hype.

I don't see that as the core topic, more of an add-on.

 

[zuz]

Again, correct me if I'm wrong, but I thought if you put a thermometer in front of a fan on a cold day it would read the actual temp.

 

[DaveC426913]

Again, correct me if I'm wrong, but I thought if you put a thermometer in front of a fan on a cold day it would read the actual temp.

Not sure how that's relevant.

Humans aren't thermometers. Notably, we produce our own heat, and we lose heat via evaporation.

 

[Tom.G]

Again, correct me if I'm wrong, but I thought if you put a thermometer in front of a fan on a cold day it would read the actual temp.

Not sure how that's relevant.

Humans aren't thermometers. Notably, we produce our own heat, and we lose heat via evaporation.

As @DaveC426913 said it's the loss of generated heat that is the problem. As an extreme example consider a heat source in a closed metal box, an electronic control system for instance. To predict the interior temperature you calculate the interior heat dissipation and use the pretty accurate 'rule-of-thumb' of 1°F rise per BTU per sq.ft. of exposed surface area. With natural convection both inside and outside the box you will be within a degree or so. If it gets too hot inside that metal box, add a fan in there. That halves the thermal resistance and the 1° constant becomes ½°; you've just cut the interior temperature rise in half by removing a stagnant air film. WInd Chill Factor?

Cheers,
Tom

 

[hmmm27]

For anybody familiar with the realities of winter, "windchill factor" is just clickbait you have to get past to find out actual temperature and windspeed. Ditto summer and "humidex".

I had the opposite problem, last week : -28C(real) at 4am and I go out for something to eat, not realizing the temperature because there's no wind whatsoever... a couple of hundred metres down the road and I had to pull over to shovel snow off the *inside* of my windshield, enough that I could pull into an adjacent parking lot and warm the engine up, to get the defrost to work... while standing outside so as not to frost things up further.

Headline a few days ago "-58F in <somewhere... North Dakota?>" which (to me) is pretty much Ragnarok, except it was just "Windchill", and nowhere in the article did it state the actual temperature.

I'm on the fence : it's a personal annoyance, but perhaps pandering to the ignorant keeps frostbite cases down.

 

[zuz]

Not sure how that's relevant.

Humans aren't thermometers. Notably, we produce our own heat, and we lose heat via evaporation.

But is it true?

 

[256bits]

I know reporting the weather is usually mundane - and what's wrong with calm ?
We need more calm-speak when a hurricane is approaching. Instead they feed hysteria

I don't mind knowing the windchill, but
Ain't that the truth. This year takes the cake for unrealistic weather reporting.
They reported few days ago that Goosebay. NL was having a bad winter with temperatures dropping to -67C.
And on top of that 10 feet of snow.
Which is BS.
Actual temperature hovers around -20C and actual accumulation in about 3 feet.
They have about 10 cm more this year of snow than average.

If course windchill hype and tall blown snow banks make better news than actual facts.

 

[DaveC426913]

perhaps pandering to the ignorant keeps frostbite cases down.

Seems a tad condescending.

 

[hmmm27]

Seems a tad condescending.

True, was rushed for words and slid a bit too far into the vernacular : "ignorant" meant in the "circumstantial" rather than "willful" sense.

I'm in a town which population is over half immigrant - the last few decades almost exclusively from regions where "snow" is just a word in the dictionary. You'd think they're the ones who need the histrionic weather reports.

But, come the first snowfall of the season, the people getting pulled out of ditches are all homegrown idjits, too confident of their or their vehicle's capabilities. Every single year, like summer resets common sense and experience.

 

[zuz]

Look in the ditch. 90% of the vehicles in there are 4 wheel/all wheel drive. Once you start sliding, all the wheels in the world won't keep you on the road. Only skill and experience will do that. And sometimes not even that is enough. 4 wheel drive only helps you get back out of the ditch.

 

[256bits]

homegrown idjits

free range idjits bike in winter snow and slush
I don't know if I have the right idjit stuff to do that

 

[hmmm27]

free range idjit

And that's going on a t-shirt, next summer.

Friend of mine, world-class (or close enough) conductor, barrels through 4 seasons on a Vespa... I think you're allowed to admire eco-consciousness and chutzpah, while simultaneously thinking somebody completely bonkers.