After a relatively benign start to winter, we have finally settled into an extended stretch of frigid temperatures. In Edmonton, some arctic air has dropped in pushing temperatures consistently below -20°C (-4°F). As I write this, the temperature outside is -34°C (-29°F) and that is a few degrees warmer than it was in the coldest hours of this morning.
It can get cold in the winter on the Prairies.
But we have a tendency to exaggerate the cold in ways that I don’t think are helpful. One of the most frequent ways we do this is wind chill.
This extreme cold snap has sparked an ongoing debate as to whether windchill numbers are useful. I am personally not a fan of wind chill numbers. Wind chill is a metric that is so frequently misused and misunderstood that I think we have a hard time making sense of what the weather actually is – especially during cold snaps.
What is Wind Chill?
If you’ve ever been outside on a cool and windy day, you would probably agree that it feels colder when the wind is stronger. But why?
Imagine that you go outside, naked, on a calm cold day. Your body will be warmer than the surrounding air and will actually lose some heat to warm up a thin layer of air around you. This means that the air right next to your skin is warmer than the general air temperature and. You actually get to exist in a thin layer of warmer air, protecting you from directly feeling the cold. Over time, your body will not be able to produce enough heat to keep this layer warm enough and you will gradually get colder and colder.
What happens if it is windy? The wind just keeps blowing away your protective layer! The heat you lost to warm that air gets swept away and you have direct contact with the cold outside air, so the air actually touching you will be colder, and you will loose skin/body heat more quickly. Unless you are outside wearing very little clothing in the depths of winter (not recommended), you aren’t really experiencing the full chilling effect that wind chill intends to account for.
The wind also helps any moisture on the body to evaporate faster. This also speeds up cooling and can make us feel colder.
In theory, when the wind chill is -30, it means that your exposed skin will feel the same as it would on a calm day at -30°C even if the actual temperature is much warmer. Because it isn’t an actual temperature, wind chill is also not typically shown with “°C” although that doesn’t stop us from confusing it with the true temperature all the time.
Wind Chill and Plants
When it comes to plants – which is one of my top cold weather concerns – I don’t bother with wind chill at all. Dormant apple trees do not produce a nice warm air boundary layer of air during the winter. They don’t really care what the weather “feels like” to humans. If it is -25°C outside, the trees above ground will likely be around -25°C already. No matter how hard the wind blows they won’t magically get colder than the actual air temperature.
That is not to say that cold dry winter winds can’t be hard on some plants, but it’s often more of a drying effect than a wind chill temperature effect.
Even if it doesn’t apply to plants, wind chill does still communicate something about the way we experience the weather. The problem is we don’t always understand what it means, or how to use it.
Problems with Wind Chill.
- Wearing Winter Clothes – Wind chill is based on how the body loses heat when exposed to the cold. At temperatures like we are currently experiencing in Edmonton, most of us are wearing protective layers and limiting our direct exposure to the air/ wind. As soon as you add warm clothes, the warm air against your skin becomes more protected. The wind chill factor can’t account for the various ways people may dress for the weather and starts to lose relevance as you have less exposed skin. Do keep in mind though, that places where skin may exposed (often our faces) will still experience the wind chill effect, even if most of our body does not. If you are planning to do a polar bear swim – it might be time to watch the wind chill a bit more closely.
- Wind Chill Stacking – People tend to start doing their own wind chill calculations and add wind chill on top of wind chill. For example: after hearing various weather reports of “-20°C, but -30 with the wind chill” many start remembering the temperature as -30°C. But what about the wind chill? We remember it was around 10 degrees colder, so it must be -40? We get too many numbers in our head, but are constantly told we need to account for wind chill. People often seem to overcompensate and become increasingly disconnected from the actual weather.
- Drama – We like to talk about weather, its generally a safe topic that everybody can identify with on some level. But those conversations are a lot more interesting when you can toss around -40 instead of -20°C. Colder temperatures are just more fun to talk about. Extended hyperbole becomes our reality and we start to perceive our weather as a lot colder than it actually is.
- Too Many Different Metrics – A number of different weather forecasts/websites seem to have their own versions of “feels like” metrics. I’ve seen screenshots from phones giving a wide range of temperatures over the last week. Depending on where you look could mean the difference between expecting -25°C outside or -50°C.
Wind chill can be useful, but we need to be aware of what it means and when it is relevant. At this moment the temperature is still -34, and the wind chill is -43. Maybe if we stopped obsessing over wind chill, we would actually perceive the weather to be warmer. If you tell somebody it feels like -40°C outside, their experience of the outdoors will probably be more intense than if you just tell them its -25°C.
I find the weather warnings that discuss how long it could take to get frostbite are a bit more useful. These warnings highlight the need to consider exposed skin, and the potential dangers of the weather without trying to replicate a temperature value.
I don’t think we are going to lose wind chill or “feels like” reports any time soon. That’s okay, but I encourage everyone to just consider how we discuss our weather, enjoy the beauty of winter, and use wind chill responsibly!