5 things to know about wind chill

Frigid temperatures have descended upon P.E.I. this week, hovering at -18 C and -19 C around the province. But it feels much, much colder — as cold as -25 or -30 with the windchill. But what is wind chill, and how is it measured?

What is it, how is it measured and why do we use it?

It's expected to feel as cold as -25 or -30 with the windchill in much of P.E.I. (CBC)

Frigid temperatures have descended upon P.E.I. this week.

Environment Canada issued a special weather statement for P.E.I. Thursday morning, warning of temperatures hovering at -18 C and -19 C around the province and winds gusting to 50 km/h. But it feels much, much colder — as cold as -25 or -30 with the wind chill.

So what is wind chill, and how is it measured? We asked CBC meteorologist Kalin Mitchell to explain.

1. What is wind chill?

Wind chill is the combined cooling effect on human skin of both the wind blowing across it and radiative loss into colder environmental air. This means that cold air and higher winds will result in a more extreme wind chill factor. Wind chill doesn't technically have a unit like temperature (degrees C) so is often expressed as "making it feel" like an equivalent temperature without the effect of the wind. For example the wind chill is making it feel near -30 today.

Wind chill is the combined cooling effect on human skin of both the wind blowing across it and radiative loss into colder environmental air. (Gary Graves/CBC)

2. How is it measured?

Wind chill isn't measured but rather calculated. The calculation is dependent on both measured temperature and sustained wind speeds. Those are typically taken from weather stations. A forecast for wind chill can be produced by combining the forecast for temperature and sustained wind speed.

3. What can a wind chill measurement tell us?

There is a link between wind chill and risk of frost bite. When wind chill values reach -28 to -39 frost bite can occur to exposed skin in as little as 10 to 30 minutes. At wind chill values of -40 or lower frost bite can occur in under 10 minutes. This risk of hypothermia also increases with more extreme wind chills.

4. Why do we use it?

We use it as a measurement to account for the combined cooling effect on skin of both winds speed and environmental temperature. It allows use to gauge the risk of frost bite and hypothermia.

When wind chill values reach -28 to -39 frost bite can occur to exposed skin in as little as 10 to 30 minutes. (Justin Fraser/CBC)

5. How unusual is this weather on P.E.I.?

While we typically experience wind chill and temperature values, comparable to the last couple of days, at least a few times during our winter season this current outbreak is rare.

It is rare both because it has occurred earlier than we typically see (January and February are when we most often get these cold Arctic air outbreaks) and that the cold with this outbreak is quite extreme — setting a number of record low temperatures in the country including at some of the newer weather station sites in P.E.I. Thursday morning.

With files from Kalin Mitchell