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Wednesday, January 8, 2014

Should We Do Away With ‘Wind Chill Factor’?

(Mel Evans/AP)

Slate columnist Daniel Engber wants to see windchill factor done away with completely. He argues it’s arbitrary. (Mel Evans/AP)

As cold weather grips much of the country, we’re hearing a lot about the “wind chill factor.”

The measurement comes from Canadian Antarctic explorers Paul Siple and Charles Passel, who in 1945 worked out an equation to show how quickly water froze at different temperatures depending on the wind.

The numbers that come out of their equation were the precursor to our modern day “wind chill factor,” which is supposed to tell you how cold it feels outside.

But Slate columnist Daniel Engber wants to see wind chill factor done away with completely. He argues that the number is arbitrary, and that factors such as sunlight, surrounding buildings and a person’s height and weight affect how temperature feels.

Critics of his argument say wind chill is a useful metric because it warns people when there is higher risk of hypothermia.

Engber joins Here & Now’s Meghna Chakrabarti to make his case against windchill.





UNIDENTIFIED MAN #1: The double-digit below-zero readings and 30-plus-below wind chills are life-threatening.

UNIDENTIFIED WOMAN: And when you factor in the wind chill, it felt like minus-40.

UNIDENTIFIED MAN #2: However, the wind chill will make it feel much colder.

UNIDENTIFIED MAN #3: We're more in the lower range, where that wind chill is between minus-30 and minus-50.


CHAKRABARTI: Honestly, just I feel frozen just hearing that. But wind chill is something a lot of Americans have been hearing about over the past several days. But what does it really mean? Daniel Engber is a columnist for Slate.com, and he's done some digging into the fascinating backstory about the wind chill factor, and he joins us via Skype. Welcome.


CHAKRABARTI: So you take us back to 1945 in your article and two Antarctic explorers named Paul Siple and Charles Passel. Who are they, and what did they do?

ENGBER: Well, these were the - sort of the originators of wind chill. They left plastic bottles of water outside in the wind, in the Arctic, and decided to see how quickly the water froze as a function of how windy it was. And they found that of course if it's very windy, the water would freeze faster.

CHAKRABARTI: So they calculated an equation off of this. American weathermen, if I understand this correctly, they converted those numbers into statements similar to what we hear today, such as the wind chill factor is, say, five below zero. But even those initially had some pretty broad inconsistencies, didn't they?

ENGBER: There were some inconsistencies. People noticed that the forecasters might say it's going to feel like, you know, minus-50, and it really - just that didn't seem right. And so in 2001, the wind chill was sort of reformed or updated so the numbers would make more sense.

But the point that I make in this piece and that I make to anyone who'll listen is that even the system we have now is fairly ridiculous and doesn't really tell you anything useful about how you might feel on any given day.

CHAKRABARTI: Well, given the weather we've been having across a lot of the country in recent days, I think a lot of people will listen to you now.


ENGBER: Right.

CHAKRABARTI: So, I mean, what about it in particular do you object to? What makes it so sort of incomprehensible?

ENGBER: Well, it makes all of these assumptions. There are these assumptions that go into the calculation that I think most people don't know about. It assumes that you're walking around outside in the dead of night, ignoring the fact that, you know, there might be sunlight. Sunlight can make you feel maybe 10 to 15 degrees warmer.

It's assuming you're walking at three miles an hour directly into the wind. It's assuming there are no obstacles around you. If you're in Boston or New York City, you're probably surrounded by buildings. It's based on wind speed readings that are taken at the top of 30-foot poles and then adjusted for an estimation of what it might feel like hitting your face at five feet above the ground. So that suggests that it's assuming that you're five feet tall.

And finally it assumes that you're overweight, if not obese, which affects the rate at which heat might escape from the skin of your face. As you can see, there are all of these assumptions that go into it. And if it's so specific to those assumptions, then why are they even telling me how I'm going to feel when I'm not five feet tall, I'm not obese, I live in a city, and I'm walking around in the daytime?

CHAKRABARTI: I had no idea that those - all those assumptions were in wind chill, I mean, because it's - in weather conditions such as we're currently seeing, it's like an almost ubiquitously used phrase. And I mean, I'm getting the feeling, Daniel, that you would just prefer it if newscasters, weathermen and -women and meteorologists in general just stopped using wind chill.

ENGBER: Well yeah, I mean, I want to make one thing clear, which is when it's windy out, it does feel colder. I mean, that's so obvious it's not even worth saying. But the numbers that are put on it are just not useful. I think they should tell you it's going to be 12 degrees and very windy, and people would know that that means it's 12 degrees, and it's going to be really cold, just as you know if they say it's 12 degrees and sunny you know it's going to be quite as bad.

So, you know, there are all these other things that the weather reporter will tell you about sun and precipitation. Of course if it's a wet and windy day, that's going to be even worse. So you get all of these factors that will affect how you feel. They're presented as individual factors. And they don't try to combine all of those into a single number that's almost certainly going to be invalid for you.

CHAKRABARTI: But if I may, though, Daniel, I mean part of what I find to be somewhat useful about wind chill is that it does give you sort of this sense that we're seeing a dramatic weather event. And in part, I mean, when the wind is blowing, and it does feel colder than usual, I mean, maybe it's a good way to say hey, be careful when you go outside because, you know, hypothermia can set in before you know it, especially in these kinds of conditions.

ENGBER: Well, there's - I sort of have two responses to that. So the first is yes, there are real dangers, and some of those dangers are exacerbated by wind. And so to highlight the fact that it's not only cold but a windy cold, and so you'll get frostbite more quickly, that's important. I just don't think that this feels-like temperature is a useful way to go about doing that. You could just say, as the Weather Service sometimes does, that exposed skin will freeze in 20 minutes given the wind and temperature.

I mean that - those are numbers that are specific and useful and are given out. I mean, these are things that would be very useful, but there are these misleading situations. So if the temperature, say, were 35 degrees, but the wind chill were 15, you're in a situation where no matter how long you're outside, you're just not going to get frostbite because the temperature is above freezing.

So you can actually create a misleading sense of risk when you start reporting these gaudy wind chill numbers that doesn't really help anyone.

CHAKRABARTI: Well, Daniel Engber is a columnist for Slate.com, educating on the ins and outs of wind chill. Daniel, thank you so much.

ENGBER: Thanks for having me.


And Meghna, we're hearing from listeners. Roger Bacon(ph) writes: Weather should be described in absolutes, no more wind chill. But I'm wondering, don't some people feel this is a competition? I mean, aren't we all trying to prove we have the lowest temperatures? So we want to know your thoughts on wind chill at hereandnow.org. Transcript provided by NPR, Copyright NPR.

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  • krkelly

    Routine wind chill factor reporting is ridiculous, if not stupid. Why not educate people on reality? For pity’s sake, most Americans still don’t understand the simplicity of Celsius degrees, and weather reporters haven’t helped to teach them. It’s time to come out of fantasyland. Weather (meteorology) is of interest to most people, to some extent, and COULD be used to promote education, rather than dumb-down everything below the lowest common factor.

    • methos1999

      Agree with most of what you say except the “simplicity of Celsius degrees” – how is Celsius simpler? I mean it’s just a different scale. I mean you could try to convince me it’s more scientifically useful than the Fahrenheit scale, but then I would counter with the Kelvin scale. After all, 0 C and 100 C are just freezing/boiling of water under atmospheric pressure, but that can change with altitude, so really quite random compared to absolute 0.

      • krkelly

        The “size” of a degree is the same in C or K (but not F). I’m fine with adding 273 if you prefer to use K. The C & K degree is based on characteristics of water which might be more intuitive than the F degree. However, I do like the added precision that tends to automatically come with the smaller degrees (increments) of F.

        • John Calabro

          I think the Fahrenheit scale follows the characteristics of human beings. 0 to 100 F is a pretty good scale of extreme temperatures for humans to experience. If the day comes when temperatures on planet earth range between water’s freezing and boiling points, then sure, I’ll change to Celsius.

    • John Calabro

      I would prefer Celsius if we were bodies of water living on a planet where the general temperature extremes ranged between our freezing and boiling points.

      I prefer the Fahrenheit scale, because its basic range of 0 to 100 pretty much matches the extreme temperature range that human beings can exist in. On either end of the scale, whether it dips to 5 degrees, or 95, you know you are going to experience extreme weather.

      I like the fact that its 0 to 100 – hey, that’s practically Metric.

      P.S. – Psychologically, there is more impact hearing that it is going to be 101 degrees five days in a row, than there is by hearing that it’s going to be a 38 degree heatwave,

  • Ward Cheney

    Perhaps the discussion about wind chill and frostbite is misguided. A more helpful focus would be on exposure, aka hypothermia, when body temperature falls below 95 degrees F. I don’t know the statistics, but I believe the number of people who die of frostbite is extremely low. Hypothermia, on the other hand, kills many more. Daniel Engber said that you can’t get frostbite with a temperature above freezing. Yet a person can die with a temperature above freezing, way above freezing.

  • jim kirby

    What we need reported are the dry-bulb and the wet-bulb thermometer readings. “Wind-chill factor” is a misused term. If the dry-bulb temperature reads -10F and the wet-bulb temperature reads -30F, it can be said that the wind chill is -30F and the wind chill factor is -20F.

    It would be dangerous to teach Amerikans to think in Celsius and understand the word “factor.” If we had an educated populace, few would turn out to vote, and we’d be ruled by the guy with the biggest family, like Romney. And if Amerikans got educated, we’d lose our public-school system, Obamacare, Social Security and Medicare.

  • Jechtech

    I wonder how much the discussion around the reporting of wind chill temps is a political one? Those people not acknowledging global climate change do not want to hear severe temperatures being reported.

    • Arfiezy

      Oh, pooh. I think the anti-CC advocates are either just plain dumb, or else their rationality is subsumed by their belief systems, or, finally, they are scared at any number of levels (what will my millions be worth? how can my businesses survive? how will i get to my Klondike hunting cabin if the frozen tundra turns to mush?).

      • Jechtech

        Having worked inside a state weather related institution for years I can guarantee you that how we report weather is very political. No “pooh” about it. Yes, the greedy are always focused only on their profits and business, but their spin masters are busy at work trying to get world citizens to accept our destructive living habits from which they prosper.

  • Jochen Dwersteg

    Report as kilocalories per meter squared per minute of heat loss.
    Over time, people will learn what this number means.

    • Arfiezy

      Ooh. Jochen Dwersteg is a smart cookie (i.e. person)! Once the number becomes famiarly known as simply an integer without its factors.

  • http://www.findingourdream.blogspot.com Hal Horvath

    I’m the perfect audience — wind chill is something I pay attention to, I think about it, I examined the tables, I’ve experienced wind chill for more than 5 minutes I suppose at least 1000 times.

    And the single point that seemed useful was that if you are in sunlight, the effective wind chill is indeed different from shade or a cloudy day.

    But otherwise, currently configured wind chill is perfect, yes *perfect* — it uses a standard and consistent set of default assumptions to deliver a reliably *consistent* measure I can count on to plan my clothing.


    So the points on the whole are just wrong. In practical terms, in the real world, for someone that experiences wind chill over and over and over.

    But it makes sense to hear this discussion, because another thing that is consistent is that NPR interviews people with ad-hoc theories that often have made-up concerns that won’t stand the test of time — those theories will entertain for a while and disappear entirely, never to be thought of again after a few days.

    • John Calabro

      Of course you’ve only experienced this ‘wind chill’ on exposed skin, correct?

      • http://www.findingourdream.blogspot.com Hal Horvath

        No, I’ve been in the cold a *lot*. I’ve experienced it on each and every last part and in just about every situation, from a too-thin jacket, to overdressed in too many layers, sweating while my ears freeze, you name it. So, I’ve experienced the real effect of “wind chill” on a too-thin coat I guess 500 times minimum.

  • Paul Schulte

    While wind chill is an interesting concept and may have some value, it is heavily overused by the media and so I am inclined to say get rid of it altogether. It seems more used for bragging rights and in many cases, the presenter neglects to point out that a temperature is not the actual air temperature but the wind chill temperature. Just report the air temperature and the wind speed and maybe add warnings about time for exposed tissues to freeze.

  • John

    By definition, any time we talk about how something “feels,” we introduce a measure of subjectivity. I’m okay with that. The wind chill is a better approximation of how it feels than the absolute temperature.
    In fact, I’d like to see the wind chill factor introduced into the summer. A windy day feels cooler regardless of the time of year.

    • http://www.findingourdream.blogspot.com Hal Horvath

      I like it that you reversed your position from an earlier comment — good brainstorming.

  • JJ

    Remember that the NFL is a not-for-profit organization. Is that why they have to charge such high prices for tickets?

  • Bill Rodebush

    I totally agree with what Mr. Engber said. It’s most annoying that the T.V. weather man takes up so much time showing what the ” feel like” temperatures are going to be, while I’m trying to find out what the real temps will be. Another thing that annoys me is that almost all of the weather people talk about what the ” Normal ” temperature is for a given date. There is no “normal” temp. It’s an “average ” temperature.

  • KPekkonen

    Using a wind chill chart is as arbitrary as using a Fahrenheit (or Celcius) temperature scale. Which is to say, it’s as arbitrary as any man made scale. When I walked my 9 year old daughter to school today, I wore a coat, hat and mittens and could still feel the chill of the air on my skin through my layers. My daughter didn’t wear a hat or gloves & didn’t even zip her coat up all the way. She felt perfectly warm as she was. The outside temperature wasn’t different for her than for me. The temperature was the same temperature, just as the windchill factor was the same for both of us. My daughter and I have always felt temperature differently, but that doesn’t mean we should throw out the standardized scales and create individual ones for each of us.

    The windchill chart has been very helpful to me in my career as an Alaska bush pilot. The metal of the airplane is certainly more fragile at lower temperatures, not lower windchills. But the pilot is affected by both. There was a day when the outside temperature at the village I was to fly to was -38F, which is cold, but not too cold for the aircraft or pilot. However, the windchill at that village was -80F..which is an insane temperature for a person to load & unload an aircraft. It could be deadly if the plane had gone down between villages. My boss wanted me to do the trip. My boss’s boss, thankfully, sided with me. I flew that day, just not to that one village. I survived to fly another day.

  • John Browne

    Daniel Engber said something Like “if it’s 35º and the wind is blowing, it doesn’t matter… you won’t freeze”. This is exactly the “uninformed” opinion which we are better off without. The wind blowing across a wet surface (your car, clothing, skin, etc) when it’s 35º will enhance evaporation… and the “heat of vaporization” will be extracted from that wet place, causing the temperature to go down. So, it IS possible to “freeze” (or experience hypothermia… the Real problem) in such cases. It’s the same principle that causes a propane tank (or cylinder) to “ice up” on the outside… even on a warm sunny day. ^..^

    • http://www.findingourdream.blogspot.com Hal Horvath

      Exactly. While I enjoy these unfinished, often random NPR interview-of-the-moment hypotheses, as they can stimulate thinking, I most often find they either don’t hold up to experience or directly contradict known science (without mention) or give us a less interesting hypothesis than the currently leading one that is already out there.
      But…..still fun anyway.
      See my other comment below.

      • jryan

        Dear Hal and John,

        Daniel said that you can’t get frostbite if the temperature is above freezing, and that is consistent with what the National Weather Service reports: http://www.nws.noaa.gov/om/windchill/windchillfaq.shtml

        -Jill Ryan, H&N

        • http://www.findingourdream.blogspot.com Hal Horvath

          Thanks Jill, but re-read. John put “freeze” in quotes, right? So he didn’t mean literally, but instead the popular usage — “it’s freezing out there” (more meaningful actually when it is not literally freezing — meant to mean: it’s like it’s freezing, even though it isn’t quite).

    • Max

      There’s a difference between freezing and hypothermia, and your statement seems to equate the two. That’s not correct.
      Skin won’t freeze at 35 degrees – period.
      One can easily experience hypothermia when it’s 60 degrees out and the person has wet clothes

  • Mollie

    I wrote up my thoughts on this Tuesday: https://medium.com/p/4673bd58554f

  • John White

    Finally! Some national attention is given to the bogus wind chill concept. Without factoring in humidity, the wind chill number is meaningless. If the air is damp, one feels far colder than when the air is dry. Direction is also a factor, walking with the wind makes one feel much less cold that walking into it, or even standing still. It is odd that weather people so love the bogus wind chill index in the winter while ignoring humidity, yet in the summer the comfort index derives from the temperature and humidity, but wind is not factored in. This is terribly inconsistent. Kudos to Daniel Engber

  • Max

    I’m an all-season outdoors guy and believe there is just a bit too much hype with with chill factor. Weathermen, always guilty of hyping the weather (justifying their existence? Ratings?) are always looking for a way to make weather dramatic. While skiing, I’ll hear someone (always a kid) saying something like “We were skiing in 90 below!”. No, it was not -90F, it was -10. Yes, it was stupid cold with the wind, but it was still -10.
    No active person I know listens to wind chill numbers at all. They *do* check the temps and wind and then dress accordingly. If you’re out for day, then you’ll always have extra clothing, anyway.

  • John Calabro

    So, hearing that it will be ’20 degrees with high winds’ is not enough for you to figure out that it’s dangerously cold? You need a chart that was fabricated out of thin air to know that ice cold is ice cold?

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