Since it is on days like these that many people mix up temperature and wind chill, here's a quick reminder about the difference, and what NOT to say...
It is very important to keep in mind that wind chill is not the actual temperature. So for example, saying ''it got down to -40°C this morning in the city'' is INCORRECT. It is so common to hear this mistake, especially in the media.
So basically, while the ACTUAL temperature was -28°C this morning, with the wind, the wind chill was -40. That means that with the wind blowing on you, it would feel like your body was losing heat as quickly as if it were -40°C with calm wind. This is because the wind takes away at the thin warm layer of air just above our skin created by our body.
But that wind chill value is felt only when the wind is blowing on you. Therefore, if you're outside and no wind is blowing on you, it would just feel like the actual temperature, which was -28°C. That is why it is incorrect to say that it was -40°C this morning, rather it was -28°C with a -40 wind chill.
There is another error associated with wind chill, which is putting a °C with the value (example: -40 °C wind chill). Wind chill is not measured, rather it is calculated using the actual current temperature and the wind speed. Since it is not measured, no units are added since it is only a value representing the COOLING RATE expressed in terms of an equivalent temperature.
Hopefully that makes sense, I tried to make it as simple as I possibly could.. =)
Bonus info... If interested, in Canada, this is the formula for calculating the wind chill: It looks complicated, but it is actually quite simple. Ta = actual air temperature (°C),
V = wind speed (km/h), and Twc = wind chill value. Just add the air temperature and wind speed in the formula then get the calculator out :)
Twc = 13.12 + 0.6215 Ta – 11.37 V+0.16 + 0.3965 TaV+0.16