Wind chill explained and what to expect late week in the Maritimes

A blast of Arctic air will combine with northwest gusts to make it feel like -35 degrees or colder for parts of all three Maritime provinces Friday night into Saturday.

There is going to be a lot of weather talk about wind chill in the Maritimes Friday night into Saturday. A blast of Arctic air will combine with what are expected to be northwest gusts of 60 to 80 km/h Friday night into Saturday to produce a wind chill making it feel -35 degrees or colder for parts of all three Maritime provinces. A wind chill making it feel -35 or colder for two or more hours is the criteria for an extreme cold warning in the Maritimes. Nova Scotia and P.E.I. haven’t had an extreme cold warning since 2015. The last one issued in New Brunswick was Jan 31-Feb 1, 2022.

So what is wind chill and why does it matter?

Our bodies lose heat to colder air via convection, which is the primary mechanism of heat transfer in gases such as our atmosphere. When we step outside into colder air, we immediately start to lose heat from exposed skin at a high rate. After a period of time, a thin, insulating layer of air develops near our skin and while we continue to lose body heat the rate at which that happens slows.

If wind is present, it will continuously disrupt or blow away that thin, insulating layer or air. That keeps the rate of heat loss from our body at a higher rate. Wind chill is a calculation of what the air temperature would have to be in order to have that higher rate of heat loss without the wind present. In the example I’m showing here, it would take a calculated air temperature of -14 C with no wind to replicate the expected rate of heat loss with an air temperature of -6 C and a 30 km/h wind. If you’d like to explore wind chill calculations for different temperatures and wind speeds, you can do so here.

As for why wind chill matters: At wind chill values making it feel -28 or colder there is an increased risk of frostbite to exposed skin. With a wind chill of -28 to -39 exposed skin can freeze in 10 to 30 minutes. With a wind chill of -40 to -47 that freeze can take place in as little as 5 to 10 minutes. Hypothermia is of course also a risk in that type of cold, unless properly dressed as well. You can find a detailed breakdown of the health hazards associated with extreme cold and wind chill here.