The sun was warm but the wind was chill
February 16, 2015 7:42 AM   Subscribe

Wind chill is vitally important information. Or is it a meaningless number useful only in making weather forecasts more dramatic?

Should a sun warm factor get equal billing? Do we need to question the whole nature of temperature? What if you're on a motorcycle? Should we just abolish winter winds? The debate continues. The only thing everyone agrees on is that the wind can strongly affect how it feels to be outside.
posted by sfenders (55 comments total) 13 users marked this as a favorite
Windchill is bullshit. Where does it go in the summer? Why do we never hear, "It's 95 out there today, but with the windchill it's 88."

I will change my mind about windchill if someone puts a glass of water outside when it's 40 degrees and the wind freezes it.
posted by flarbuse at 7:46 AM on February 16, 2015 [8 favorites]

Daniel Engber's piece at Slate is a joy to read but I heartily disagree: I've found wind chill numbers to be helpful in gauging extreme winters in Philadelphia and besides, if you're a weather geek and love stats, it's another stat to look at.

This is like a perfect post, btw.
posted by joseph conrad is fully awesome at 7:47 AM on February 16, 2015 [3 favorites]

Wind chill is a real phenomenon, but the wind chill factor is a problematic characterization of the effect, confounded by variables like putting a damn hat on.
posted by cardboard at 7:49 AM on February 16, 2015 [9 favorites]

Perceptual conditions would best count in all four factors: Ambient temperature; Windspeed; Humidity; and Radiant energy. A hygrometer get's you three out of four, there are sensors for all of this, that set of data is the comfort level.

No reason that it can't be sensed relativistic to a framed position such as mounted on the motorcycle.
posted by StickyCarpet at 7:52 AM on February 16, 2015 [2 favorites]

I've always had a hunch wind chill was a fake way of altering a real thermodynamic measurement (temperature) for the sake of headlines/news attention/clickbait. It's kind of like the sit-to-wipe vs. stand-to-wipe argument, though - both sides are entirely convinced they're right, even though one is clearly the obvious winner.
posted by rubadub at 7:53 AM on February 16, 2015

Hm, this makes me wonder what actual units of measurement one would use for wind chill. It's not strictly temperature or even a thermal measurement. To the googles!
posted by surazal at 7:56 AM on February 16, 2015

Windchill's definitely there in the summer. Try being on a sailing boat in strong summer winds, which can be cold. Or a mountain top. I've been both and seen people affected to the point of physical impairment, and worry for the rest of us there. It's not about glasses of water, it's about the body's physiological response.
posted by dowcrag at 7:57 AM on February 16, 2015 [34 favorites]

Oh, and for true comfort level measurement there are other real factors such as expectations, for example the nature of applicable seasonal clothing. It will seem colder if I am rightly wearing a white linen suit at the time, versus wearing my ski gear.
posted by StickyCarpet at 7:57 AM on February 16, 2015

No, knowing that it says that it's -2 out, but really it feels like -20 really is important to know in order to figure out which damn hat to put on. Sometimes there really isn't a wind chill, and the difference when it is -2 and feels like -2 is very refreshing.

People who care about the sun warm factor must live in places with more sun in the winter than Minnesota. It does make a difference, but mostly for an hour.
posted by dinty_moore at 7:58 AM on February 16, 2015 [12 favorites]

Oh, and for true comfort level measurement there are other real factors such as expectations, for example the nature of applicable seasonal clothing.

Well, obviously, yes. Putting on extra clothes will keep you from being so cold. The wind chill number just helps you to figure out how many extra clothes to put on, it's not meant to suggest that you will feel precisely that cold at all times.
posted by jacquilynne at 8:03 AM on February 16, 2015 [1 favorite]

Speaking of meaningless and misleading numbers.

Fun game to play with others:

If someone mentions that they're cold, pick a part of their body that's uncovered and tell them to cover it, explaining that you lose 80% of your heat through that body part.

"You should put on a hat, you lose 80% of your body heat through your head."

"You should put on some socks, you lose 80% of your body heat through your feet."

"You should put on a scarf, you lose 80% of your body heat through your neck."


I do this all the time and it's nearly always met with, "yeah, I've heard that" while the person bundles up.

"You lose 80% of your body heat through your eyelids."
"Yeah, I've heard that."

See how ridiculous you can get!
posted by phunniemee at 8:04 AM on February 16, 2015 [12 favorites]

Just wanted to tip my hat to you for the Robert Frost reference. If only we had made it to mud-time by now...
posted by Miko at 8:04 AM on February 16, 2015 [1 favorite]

Nobody who has ever lived in Minneapolis would question that wind chill is a thing, except there it is "wind feels like somebody is throwing a bag of frozen hammers at you."
posted by maxsparber at 8:06 AM on February 16, 2015 [9 favorites]

Mythbusting the 80% through your head story.

At the same time, it's real enough. Back when I worked as an outdoor educator, year-round, part of what I had to do was not only dress for a 12-hour day outdoors, in January and February, in Massachusetts, but also help kids get ready for it. And often they were kids who had not been taught good practice in dressing for winter. Covering everything you can is just essential, and the windier it is, the more you need that cover. The head makes a lot of sense to cover as a priority, because it's so full of tightly packed blood vessels near the skin and that means they can easily lose heat to the environment if not insulated - more so than, say, your elbow or whatever. Over those years I definitely learned that if I have warm socks and shoes and a warm hat on, I could get away with very light layers on the rest of the body and sometimes even skip a coat, if my sweater or fleece was windproof enough. The hat makes a big difference. Mittens and gloves as well - total necessity. Whether or not the neck needs covering, to me, has a lot to do with wind chill.

Later on, I did a lot of work around fishing history and fishermen. One of the women fishermen I worked with had a saying she told all her rookies: "if you're cold, you're dumb." Basically, that feeling cold is an entirely preventable condition, and that by having the right gear and not beeing too tough-guy to wear it, you can prevent it almost completely.
posted by Miko at 8:11 AM on February 16, 2015 [7 favorites]

Wind chill does matter. I was out walking my dog yesterday, and when the wind was in my face it was painful; when it was at my back, merely cold. Sure, it is a measure of how fast cooling happens, it doesn't make things colder--but it matters to me whether I will get frostbite in 10 minutes or in an hour. When the wind is strong the mammalian internal heating system can't keep up.
posted by librosegretti at 8:13 AM on February 16, 2015 [4 favorites]

Being a bicyclist I know wind matters. On a day I play tennis in shorts and a tee I need a lot more bundling to cycle home at 15 mph.

I've also been out in 60 degree weather watching a bike race in huge wind and thought I was going to freeze.

I don't know if the weather reports windchill is useful, but it sure is real.
posted by cccorlew at 8:14 AM on February 16, 2015 [1 favorite]

Well, obviously, yes. Putting on extra clothes will keep you from being so cold.

Not just that. Even observing the clothes that others are wearing around me will affect how I perceive the temperature.

I spent some time with various recording sensors indoors, and it is quite interesting how one's guesses compare to the data. Just after the sun goes down people will register indoor temperature as being slightly cooler, even though the sensor does not.
posted by StickyCarpet at 8:19 AM on February 16, 2015

Where does it go in the summer? Why do we never hear, "It's 95 out there today, but with the windchill it's 88."

Because your skin is at, oh, 80F.

Fundamentally, cooling is the transfer of heat from something that warm to something that's cool. It doesn't go the other way. One of the big factors is how fast something cools is the temperature differential -- things that are 100F in 30F air cool faster than things that are 50F in 30F air.

When your body warms up the air in still air, you build a boundary layer around your body, which slows heat loss. You lose that layer slowly, because of convection, since hot air rises, but once you get that layer in place, you cool slower. SCUBA divers know this from wet suits, which trap a layer of water right next to the skin, which warms up, and that reduces the temperature gradient and the heat loss.

But that's still air.

In a wind, you warm up the air around you, but that air is then pushed away by the wind. So, with a wind, your skin loses heat faster. This works in summer as well -- just sit in front of a fan. The faster the wind blows, the faster that warmed air is replaced by fully cool air, and the faster the heat loss from your skin. In addition, you get moisture evaporation. Your body attempts to keep the body temp constant, so you don't reduce the skin temp dramatically until the heating effect is overwhelmed.

Wind chill, against unprotected skin, is a *very* real thing. The idea of winter clothing is exactly the same as the idea of the wetsuit in diving -- trap a layer, warm it up, reduce the heat loss.

Now, unheated items don't really see wind chill after they reduce to ambient. If they're at -14F, and the air is at -14F, and they're dry, they won't cool below ambient no matter how hard the wind is blowing. The wind will *help* them drop to ambient quicker, but once you're at ambient, as long as you're not evaporating water, you'll stay at ambient. If you are evaporating water, you can drop below ambient (see "wet jeans" for a real example.)

People who spend time in high apparent wind conditions -- cyclists, sailors, convertible drivers, etc. -- know this effect well. They even see it at far warmer temps that you do if you're standing still.
posted by eriko at 8:26 AM on February 16, 2015 [38 favorites]

In my experience humidity has also been a big factor in perceptual coldness. When skiing in the west vs. the east, that extra humidity seems to take the heat out of your bones much more quickly.
posted by RobotVoodooPower at 8:33 AM on February 16, 2015 [3 favorites]

Don't we get a "sun warm" factor? Forecasts in the summer often talk about heat index or the difference between temperatures in the sun and the shade.
posted by that's how you get ants at 8:34 AM on February 16, 2015 [5 favorites]

Wind chill is real, but I wish they would describe it more accurately.

Temperature: 0°F
With Wind Chill, Feels Like: the moment you realize we all live alone and we all die alone.
posted by logicpunk at 8:38 AM on February 16, 2015 [36 favorites]

My ears got mildly frost bitten yesterday, as the result of a 10-minute walk with an inadequate hat.

My own idiocy is partly to blame, but wind chill is not fucking around.
posted by TheWhiteSkull at 8:42 AM on February 16, 2015 [5 favorites]

From Miko's OSU link:
What my mom was worried about, of course, was the dreaded frostbite, of Jack Frost nipping at my nose. What exactly would put my nose (or ears or toes) at risk?

Environmental: Prolonged exposure, extreme cold, damp cold, high altitude. During severe cold, frostbite can develop in a matter of minutes. Everything that is exposed is at risk. Feet and hands are affected most frequently, but ears, noses, cheeks, and even corneas are also at risk. I challenge you to find a hat for your cornea.

Poor underlying health and/or altered mental status: Prior cold injury, alcohol use, tobacco use, malnutrition, diabetes, peripheral vascular disease, and severe mental health all limit the body’s ability to respond to any severe stress, including cold temperatures. Of note, prior cold injury can quadruple the risk of a subsequent cold injury.

Clothing: Inadequate clothing obviously increases exposure. But constrictive clothing that limits blood flow to the extremities, toes, etc. also increases risk of cold injury.

Being male: Whether this is because of some kind of genetic susceptibility or because males tend to spend more time outdoors isn’t clear. African American males appear to be at special risk. During both the Korean and Falkland Wars, there was a higher prevalence of frostbite in African American men than in other similarly attired races.
That would be me alright. Go out with a hat on, I'm fine. Go out without a hat on, for as little as a couple of minutes, and I will be sick. Hairstyle plays into that some I'm sure.
posted by cashman at 8:42 AM on February 16, 2015

Oh sweet baby jesus please don't let this information get to the rest of my family. My family are weather obsessed. OBSESSED.

Part of this was growing up in a mobile home in tornado alley. If the weather got iffy we dashed to the car and drove over to my grandmother's house to sleep. Having my parents move to NOLA and get their house destroyed by Katrina didn't help either. There's still a ton of PTSD and anxiety to deal with, nearly 10 years later.

But every time I call my parents, or even my grandparents, a good 10 minutes is spent discussing weather. First the weather they're having, the weather they've had, and then on to the weather that I'm having, and the weather that I'll be having in the next few days, and then, you know, how the arctic stream or whatever is going to move that weather their way in a day or so and they're going to see the pressure drop one, maybe two quads. So we're going to run a matrix on the firewall to hold off the rain capacitors and blah blah damn dad, I get it, there is weather.

Personally, I love the WeatherUnderground app. Open it and it says "Today will be cooler than yesterday. 40% chance of rain." Cool! Everything I need to know!
posted by spikeleemajortomdickandharryconnickjrmints at 8:46 AM on February 16, 2015 [1 favorite]

In my experience humidity has also been a big factor in perceptual coldness.

Oh, yes. -30 C in the prairies - actually not that bad, given the sun and dryness, as long as you dress appropriately. -15 C in cold-swampy/windy/usually sunless Toronto - wanting desperately to jump outside of your body and leave your shaking bones behind.
posted by cotton dress sock at 8:51 AM on February 16, 2015 [5 favorites]

People who spend time in high apparent wind conditions -- cyclists, sailors, convertible drivers, etc. -- know this effect well.

Absolutely true. I'll never forget a July day spent out catamaran sailing (read: getting wet) on about a 76-degree in day in Michigan. It got overcast, the wind was whipping, and damned if we didn't start getting hypothermic. We actually had to pull up on the sand and make a fire to dry our clothes and warm up. And it was a beautiful day for most people who were on land - but out there in cool water with wind whipping, we just couldn't stay warm and were starting to stiffen up.
posted by Miko at 8:53 AM on February 16, 2015 [1 favorite]

Wind chill is terrifically useful for telling HOW LONG it will take exposed skin to get frostbitten when it's below freezing out, which is vital information for deciding whether to cancel school because kids can't safely be at bus stops. Its easy for laymen to understand and NWS provides us pretty charts to help.

Otherwise it's mostly for bitching about how cold it is out and berating my husband for not wearing enough layers.
posted by Eyebrows McGee at 8:56 AM on February 16, 2015 [3 favorites]

Wind chill frostbite chart. Pretty colors! Easy decisions! Everyone understands it!
posted by Eyebrows McGee at 8:58 AM on February 16, 2015 [5 favorites]

Wind proofing is the best defense against wind chill. I notice jeans are basically useless for warmth on a windy winter day but add the lightest layer of long johns underneath they become super warm. Same goes for jackets, a fleece is useless as the wind rips right through it, but add the lighest rain jacket you are ready to work in 15 degree weather. I find layering to be much more value than wearing a heavy coat when working/cycling outdoors. Sweat is your greatest enemy and these days I'm shoveling outside every week and find it a fun game to see how much I can shovel without actually activating my sweat glands. I often make it down to my t shirt in 20 degrees. Another great trick on a sunny cold day is to take my laser thermometer and point it to the ground getting hit by the sun. Often the temp will be as much as 15-20 degrees warmer so I can dress for 50 instead of 35 if I don't plan on being out past sundown.
posted by any major dude at 9:00 AM on February 16, 2015 [1 favorite]

You can pry the wind chill forecast out of my cold, dead hands (that became that way because there was no wind chill forecast and the quickly moving cold air rapidly removed heat from my body).
posted by the jam at 9:17 AM on February 16, 2015 [4 favorites]

So I am really bad at translating temperature into how cold or hot it feels. I never fully learned celsius and fahrenheit because I grew up in a hot and dry climate that used F, then started my adult life in Toronto where they use Celsius and it can be really cold in winter and really humid in summer. So all the lower Fahrenheit readings are completely meaningless to me (20? -10? 0?) and the higher Celsius readings are basically meaningless (20? 30? 40?). Now I live in NY and I switch my weather app to be F during the summer and C during the winter. In spring and fall I basically have no idea what temperature it is. I've tried to teach myself what the colder F temperatures mean in terms of how cold it feels, but I find the windchill is so variable it's almost a pointless exercise.

My ideal phone app - and someone tell me if this exists - is something that would tell you the YESTERDAY windchill/humidity adjusted temperature at the current time (e.g. 7AM), then show you TODAY's temperature. In other words, just tell me if it is colder/more windchilly or hotter/more humid than this time yesterday.

The weather app on my phone (I use the little blurb in iPhone notifications) doesn't tell me the windchill/humidity adjustment, so for me the temperature readings are just meaningless numbers. In fact, sometimes it doesn't tell me the temperature at all. Today it just says "sunny."

And windchill is super important. Last night here in New York there was even a windchill advisory where they specifically said you could be at danger of frostbite or hypothermia due to windchill. Who cares what temperature water freezes? When I lived in Canada I used to joke that Celsius is the ideal temperature system for science and Fahrenheit is the ideal temperature system for describing the weather, because in most of the inhabited world ~100F is the hottest it can get and ~0F is the coldest it can get.
posted by pravit at 9:20 AM on February 16, 2015 [2 favorites]

Yeah, I think they should just cut to the chase - I mean, they should mention key metrics, for pilots' and farmers' sake - but I think most of us just need to see a little guy wearing whatever you're supposed to be wearing to prevent frozen flesh or soggy feet etc.
posted by cotton dress sock at 9:30 AM on February 16, 2015

But every time I call my parents, or even my grandparents, a good 10 minutes is spent discussing weather.

This is called being British.

Windchill is a real thing, I've worked outside at - 35C with and without wind, without wind is a lot more bearable.
posted by arcticseal at 9:34 AM on February 16, 2015 [1 favorite]

Having grown up in Ottawa, no one gives a flying fuck about making the cold sound more dramatic than it is. It is what it is, and it's fucking cold. February usually worst of all.

I used to have to walk up a road to get to high school that was in a bit of valley, with an overpass going over it. The wind would shoot up this street very hard, very fast. And it felt much, much colder than the walk to get to that street. On that particular stretch of the walk, you could expect your eyes to water and then your tears to freeze on your eyelashes. Sometimes the top ones would freeze to the bottom ones, but it didn't matter much because you'd be squinting anyway. You could expect your scarf to freeze and harden like a mold of your nose and mouth as the vapor from your breath collected and froze. If you didn't fully dry your hair that morning? Even with a toque on, your hair would freeze in clumps that felt like you used a lot of hair gel and applied it poorly. None of this happened without that wind. I don't know if "wind chill" captures this effect appropriately enough for scientists, but it was a useful "if you're walking into the wind, cover everything" warning at least.

Should a sun warm factor get equal billing

Yes. I live on the Pacific coast now and it is the first place I've ever been where the air is usually kind of cold even in summertime, but you feel quite hot in the sunshine. Move under the shade of a tree? You're cold. Walk around in the sun? Sweating. It sounds useful to me.
posted by Hoopo at 9:37 AM on February 16, 2015

The Scientific American article (linked under Wind Chill) includes this bit about a system that factors in exposure to the sun: 'AccuWeather’s “RealFeel” index adds in effects such as cloud cover and sun angle, but because the formula is patent-protected outside scientists cannot evaluate the math.'
Some of the components that are used in the equation are humidity, cloud cover, winds, sun intensity and angle of the sun. Humidity is a large contributor to determining the RealFeel, but the time of the day also is important, due to the angle of the sun.

In the morning the low angle of the sun gives off less heat because the energy is spread out, according to Expert Senior Meteorologist Dan Kottlowski. In the afternoon, the sun is overhead and the sun's energy is more direct and gives off more energy, making it feel warmer.
posted by achrise at 10:15 AM on February 16, 2015

...bullshit. Where does it go in the summer? Why do we never hear, "It's 95 out there today, but with the windchill it's 88."

Anybody who's ridden in the desert at 95+ degrees knows that a 'wind chill' makes a BIG difference between a ride in which both rider and horse perform happily and safely versus one which could compromise rider/horse welfare, or at least make for a miserable ride.
posted by BlueHorse at 10:18 AM on February 16, 2015 [1 favorite]

In developing the wind chill index, volunteers had to have a measure of core temperature. So, running around in the bloody freezing with a probe up their butt. Nopenopenope.
posted by scruss at 10:33 AM on February 16, 2015

Windchill, yes. Working in construction I can tell you that -15C without wind is waaay better than working at -10C with wind. That feeling where the air hurts your face? Windchill. If there's no wind things are a lot more bearable.
posted by Vindaloo at 10:34 AM on February 16, 2015 [1 favorite]

From the Slate article:

In the 1970s, the Canadian weather service started reporting numbers based on Siple and Passel's work. These three- and four-digit values meant little to the average person, however—the "wind chill factor" might have been 1,200 one day and 1,800 the next.

As someone who grew up with these numbers on the weather forecast: bull. Sure, it's a number in arbitrary units. So are temperature, windspeed, and barometric pressure. After a couple of Winnipeg winters, you knew that 1200 was just fine to be outside in, while 1600 was getting uncomfortable, 1800+ meant risk of frostbite, and 2000+ meant we got to have recess indoors.

Ironically, having moved to the US now, I find the temperature-equivalent windchill values less useful to me, for many of the same reasons stated in the article. I often wish that I could find a website that still provides the cooling-watts-per-square-meter number, just so I could look at it and think "indoor recess!" for a split second.
posted by Johnny Assay at 10:49 AM on February 16, 2015 [1 favorite]

I remember I saw a link to a video from some weather service on how they generate their feels like temperature, and I thought, "Great! This should explain how they synthesize wind chill, heat index, and whatever into a single number!" But then I watched it and it was just a two part video explaining what wind chill and heat index are. I was displeased.
posted by ckape at 11:14 AM on February 16, 2015

The reporting of wind chill carries with it a paternalistic impulse to explain not just how cold it is, but how cold we'll feel. Well, I've been out in the cold every day this week, and I know exactly what it's like.

It's almost as if the weather report is meant to tell people who don't necessarily have experiential knowledge of the current temperature what the weather is! What a crazy concept!

Namely, they geared their calculations toward people who are 5 feet tall, somewhat portly, and walk at an even clip directly into the wind.

Technically they're looking at 5 feet as the average height of the face. If the top-of-head to "face" (let's say nostrils?) is 6 or 7 inches, that's only off by a couple of inches. Pretty accurate, and Slate can't manage to get the measurement used correct.

That is some garbage anti-science bullshit. Look out the window and we can all judge what the temperature will be? Sure, except for anyone who's recently moved to the region, who's travelling to the region, who lives in a basement that they can't really see out of because of the snow, who lives in a dense urban area so they can't see anything but other buildings.

(and the hotness-analogue of windchill is probably the Humidex, which measures how hot it feels based on temperature & humidity)
posted by Lemurrhea at 11:19 AM on February 16, 2015

Wind chill numbers to stress the importance of realistic precautions on days that the cold could kill you and heat index numbers to stress the importance of realistic precautions on days that the heat could kill you both seem less like bullshit and more like a useful public service to me, regardless of the inconsistency of not using those modifiers when temperatures aren't at an extreme.
posted by jason_steakums at 11:23 AM on February 16, 2015 [5 favorites]

My problem with wind chill as it is currently used is people don't understand that it is only useful as a rate of cooling rather than a indication of ultimate temperature. So they'll plug in their car when it is -5 but the wind chill is -25. Even though they would not plug in at an unmodified -5.
posted by Mitheral at 11:51 AM on February 16, 2015 [1 favorite]

I stepped outside in Brooklyn yesterday morning during a brief pocket where there was no wind blowing. As "wind not blowing" isn't something of which one takes any notice, all I noticed was how bright the sun was and surprisingly pleasant the temperature. I threw a coat over a t-shirt and headed out to meet up with my GF for a day that was sure to promise a shitload of walking around outside.

The trouble was, on this day when I was never fewer than two subway transfers away from home, the wind turned out to be blowing roughly 99.9% of the time, and when it was blowing, the temperature dropped from "surprisingly pleasant" to "firehose of ice and rusty nails."

So I don't know about the accuracy of any numbers they give you, but if the wind is going to make going outside feel like staring into the face of God and coming to grips with every poor decision you've made in your life, I'd like to know that before leaving the house.
posted by Navelgazer at 12:19 PM on February 16, 2015 [1 favorite]

"It's not about glasses of water, it's about the body's physiological response."

No, that's wrong. The explanation for "what it feels like" has misled even people who think they understand wind chill. It is an objective, not subjective, phenomenon.

As eriko explains, wind chill is essentially about the rate of heat exchange. It does affect glasses of water because the whole idea is that your body or the glass of (relatively) hot water heats the air around it, the air is blown away, the air that replaces it is heated, and so on, which increases cooling. It's exactly like blowing on hot soup. Without air circulation, the air immediately around something is raised to nearly the temperature of that hotter thing, that air just sits there, and the heat transfer slows down. The greater the temperature differential and the greater the air flow, the faster the cooling occurs.

This is why fans cool people but not rooms -- we're hotter than room temperature and without the fan circulating the air, we just raise the temperature of the air immediately near our skin to closer to body temperature and we feel hot. And that's the case because our metabolism is set up to dump heat to the cooler environment and so an environment at body temperature or greater is uncomfortably hot to us.

They talk about "what it feels like" because we don't sense temperature directly, we sense heat transfer. I think probably most people don't understand this. A thermometer measures temperature directly, while our bodies don't sense relative temperature but rather the rate of heat exchange -- which is good enough because generally the greater the differential, the greater the rate of heat transfer. Also, we don't even sense the rate of heat transfer generally; but instead have separate thermoreceptors for loss of heat (coldness) and gain of heat (hotness).

That we sense the rate of heat transfer rather than the temperature is why, for example, metal surfaces seem both colder and hotter than other surfaces and why even when everything in a room is at that same ambient temperature, the metal pan and the wooden bowl don't feel like the same temperature to us when we touch them. This is because our bodies aren't at room temperature and so when we touch a 76F degree metal pan, heat moves from our finger to the pan much more quickly than when we touch a 76F wooden bowl.

Back to wind chill, even though it's an objective fact of heat exchange, assigning a number to it requires making a whole bunch of generalizations. The heat exchange in any particular example is going to depend not only upon the temperature differential and the wind speed, but also upon the characteristics of the air (such as its humidity), the specifics of the air flow around the body and the environment, and the specifics of the body and clothing. So for any given person, the "feels like" number will be more or less accurate relative to how closely their particulars match the generalizations.

Finally, given that we're talking about heat transfer being affected by air flow, and about human body temperature and ambient air temperature and wind, then you might think that this would mean that when the air temperature is greater than body temperature, then more air flow will increase how hot it feels. But this generally isn't actually the case because in hotter air we rely upon perspiration to cool us down. And the rate of evaporation of water is heavily dependent upon how humid the air already is -- so in a drier environment, such as a hot desert, where the air temperature is higher than body temperature, it will still help to have wind because most of the cooling of our bodies is occurring via the evaporation of our sweat and that depends upon getting the more humid air in which we've dumped our body heat via evaporated perspiration away from our body so more perspiration can evaporate. So in a wide range of conditions, air circulation cools us down. (However, in a very humid environment where perspiration isn't cooling us very much at all, then if the air temperature is greater than body temperature, more wind won't help at all.)
posted by Ivan Fyodorovich at 12:27 PM on February 16, 2015 [11 favorites]

I do wish that it was more accurate but i've never used it as more than a guideline anyway. The weather people up here in North Dakota take it pretty seriously which they should. Nothing like stepping outside and that wind that swung down from the Arctic steals the air right out of your lungs. There's cold and then there's that situation. It's gawdawful. So when anytime the weather kids start warning about windchill below minus twenty I take notice. Minus fifteen, that's just normal winter weather.
posted by Ber at 12:37 PM on February 16, 2015

Finally, given that we're talking about heat transfer being affected by air flow, and about human body temperature and ambient air temperature and wind, then you might think that this would mean that when the air temperature is greater than body temperature, then more air flow will increase how hot it feels. But this generally isn't actually the case because in hotter air we rely upon perspiration to cool us down.

With my motorcycle helmet on there were definitely days when opening the visor felt hotter than leaving it closed. This a special case, but does happen.
posted by TheJoven at 12:52 PM on February 16, 2015

Having a cabin in the Adirondacks where the actual tempature is often -15F or colder, wind chill never meant much to me. You dress to cover your entire body even your face if you can. I have walked across a frozen lake with the actual temp well below zero F and with wind chill below even that. Figgin cold is friggin cold. The only difference is to the tears in your eyes. The wind causes more tearing.

What my sons and my friends who have come to the cabin in February don't get is that going from -20F to +20F is a 40 degree difference in temp. They just assumed it was cold either way, but if you went from 20 degrees F to 60 degrees F you would feel the difference. You will open your jacket to let some air in if you go from -20F to 20F.
posted by 724A at 1:01 PM on February 16, 2015

My own experience is that there's kind of a change at around -10F. There to about 20F is cold, that's true, but below -10F (-23.3C) it's bitterly cold where moisture in your nose quickly freezes and just stuff that seems actively hostile. In the other direction, I feel the same way about, say, 110F in a dry heat (98F in a humid heat) where below that it's hot, even intolerably hot, but not so much like nature is trying to kill you. Below -10F and above 110F is just meteorological hostility.

The air seems different to me when it's -10F or below.
posted by Ivan Fyodorovich at 1:57 PM on February 16, 2015


posted by TheWhiteSkull at 3:02 PM on February 16, 2015 [2 favorites]

My cold story, which I don't think I have told on the Blue before.

In 93 I worked in Flin Flon Manitoba from January to April. When I got there, the sun came up after 830 am, you could feel the hairs SNAP in your nose when you breathed, and on a really good day spit would freeze on the way down to the ground. The entire town was full of electrical outlets at parking spaces to run your block heater, but it didn't matter because a lot of folks just left their engines running when they stopped for groceries etc. anyway.

Layering was the key, including padded flannel workshirts and jacket liners under jackets under coats, and hats over hats etc.

Towards the end of my stay I had developed a habit of sticking my head out the back door while I was brushing my teeth to gauge the state of things. One day in mid april I thought, huh, not too bad today, and started walking to the mill (20 min away by foot) in a t-shirt and thick flannel workshirt. Halfway there I took off the workshirt. Got to the main gate, where there was a large clock and thermometer on display, and it was minus 5 Celsius.

and that's when I knew it was time to go back to Ontario.

Oh, but dryness made a huge difference, no doubt.
posted by hearthpig at 6:04 PM on February 16, 2015 [6 favorites]

This thread seems like a good place to post the Mount Washington Observatory boiling-water-to-snow trick they like to do up there whenever it gets really butt-cold. Why not throw in some frozen soap bubbles, too. And why not a little more about how freaking cold it is up there.
posted by Miko at 6:45 PM on February 16, 2015

Oh, but dryness made a huge difference, no doubt.

I dunno. Some of us, who grew up with frozen snot and block heaters and snow pants for Halloween, were able to build snowmen as tall as us with our bare hands on a bright, dry, -25C prairie day, yet found ourselves perplexed when we got to Ontario, where no matter how thick the coat, -10C meant we just could not stay warm. (Although, whether that's to do with the weather is debatable.)
posted by cotton dress sock at 6:52 PM on February 16, 2015

I slept with a canteen of snow hoping it would be water by morning. March camping in Arches is a crapshoot. The wind came up in the middle of the night, we moved the tent up against the Anasazi rock shelter, got out and under the rock to block the wind. Next morning the canteen was still frozen, we climbed up to the cliff face for sun, the rock was booming as it warmed. We went for what was upposed to be a quarter mile to Upheval Dome, but wandered, and I realized my tall, thin fit manfriend was confused, then weak, I put his arm around my shoulder and half carried his hypothermic form up and out to the car. I turned up the heat, tucked him in, in the back, he slept all the way back to SLC. The night wind did us in.
posted by Oyéah at 9:48 PM on February 16, 2015

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