Monday November 24, 2014

Is the wind chill full of hot air?


This time of year is not only cold in the weather sense, but it’s almost as if the news has gone into a deep freeze as well.

For this week’s paper, I was relegated to manufacturing stories. I don’t mean making up news, but basically spinning even a germ of an idea into something to write about.

Unfortunately, one of those germs was the recent spate of sub-Arctic weather gripping the prairies. You might be surprised how difficult it is to obtain reliable quantitative data on how this winter stacks up to winters past. There are so many factors, it’s hard even to definitively say something non-committal such as “one of the coldest winters on record.”

Qualitatively, however, few Yorktonites would disagree that it has been a particularly bitterly cold one so far. When school buses aren’t running, when the Coop won’t even pump your gas for you, it’s a pretty good indication Old Man Winter has settled in with a vengeance.

In doing the research to try to eke out some kind of cold winter story, I came across an interesting little news item about Environment Canada (EC) changing the way it reports cold weather.

Currently, EC issues wind chill warnings when the combination of air temperature and wind speeds exceeds the health-threatening threshold (-40C).

The problem, according to the federal weather agency, is that they currently do not issue warnings if the temperature drops into that range without wind. As early as this year, EC will stop reporting temperature and wind chill separately, rather include them together in a new Extreme Cold Warning, which will be linked to information on how people can protect themselves.

To be honest, it took me a while to wrap my head around this. Why change something that seems to be working just fine. As Canadians, perhaps none more so than prairie people, we pretty much take it for granted that we get it. Apparently, Environment Canada doesn’t think we do. And, they may be right since around 100 people die every year from cold-related causes.

To get a handle on it, I went back to square one. How does wind chill work? It’s a pretty simple concept, right? We all know that when it gets into the minus-30s, wind or no wind, skin can freeze in pretty short order (10 to 30 minutes according to EC).

We also all know that wind exacerbates the problem, not by actually making the air colder, but by stripping our body heat more rapidly, the same way blowing on a spoonful of hot soup helps it cool more quickly so it won’t burn our mouths.

And we all know that there is some kind of complex math formula that uses a combination of air temp and wind speed to calculate how cold it would have to be with no wind to cause the same degree of heat loss.

Of course, as soon as I had to write this down, I started to see how it can be a bit problematic. It is not a measure of how cold you will get if you stay out too long, but an approximation of the rate at which you will get there.

It is simple on the surface, but as you drill down into the nuts and bolts of wind chill, you start to quickly see its limited utility. In the first place, it assumes some hypothetical average person, (who apparently is five feet tall, a tad portly and walks at a steady pace into the wind). It also assumes a steady (or average) wind speed, but we all know wind is extremely variable.

There is also the misleading “feels like” moniker weather forecasters have opted for in recent years, presumably to avoid changing how they report weather from summer to winter. Quantifying how even a hypothetically average individual experiences weather seems a bit of a fool’s errand, however, particularly since there are other factors left out of the calculation. For example, on a sunny day, we will feel warmer than on a cloudy day with the same wind chill.

Another misleading aspect of using temperature equivalencies is that it is always the real temperature, not the wind chill that carries the health risks. To illustrate this, take a very windy day with an ambient air temperature of 1C and a wind chill of -11C. No matter how long you stay out on a day like that, your skin will not freeze; at a real temperature of -11C, it eventually could. But, even at 1C, there is danger of hypothermia, which occurs when our core temperature drops just two degrees from 37C to 35C.

Similarly, although a day with a wind chill of -40 may be unpleasant and will ultimately kill you, a day with an actual temperature of -40 will kill you faster.

So, it looks like Environment Canada might be on to something with its new system, but ultimately our best defence against the cold is our own experience. Those of us who have grown up with these conditions have a pretty innate sense of what we can take and how we need to dress depending on what activity we plan on engaging in.

My favourite story to tell about this involves some friends from Dallas, Texas, who were visiting Ottawa. It was their first time in Canada during the winter and they were worried about the frigid horror stories they had heard. The day they arrived, though, was extremely pleasant for February with the temperature hovering just around the zero mark.

We went to Winterlude, Ottawa’s annual winter festival, surveyed the ice sculptures, skated on the Rideau Canal and had Beaver Tails. “This isn’t that bad,” one of them remarked about the weather.

When we parted that evening, they asked me what I would recommend for brunch the next day. I suggested they should go to Chinatown for dim sum as it was a short walk from their hotel.

Unfortunately, overnight the temperature dropped to the -30s (-40s with the wind chill). Just after noon, I answered the phone. “What the [expleted deleted] is wrong with you people; how do you live here?” my friend shouted.

She explained they had left the hotel to walk to Chinatown and quickly turned back as they experienced their first brush with an Arctic blast. I felt bad because it had not occurred to me they might not have the common sense—why would they, they were from Texas?—to check the weather before they left.

“What do you do when it gets this cold?” she continued.

“I’ll tell you what we don’t do,” I replied. “We don’t try to walk to dim sum when it’s minus-40.”



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