This morning we had a very good example of what the wind can do on a chilly day.  This morning low temps fell to the mid 40s in Austin, but when you factor in the 15 mph wind, the Wind Chill value fell to about 38.  By contrast Sunday morning we will have temperatures in the upper 30s with little to no wind, so Wind Chill values will be in the upper 30s too.   If you ask me, I will always take the colder air with no wind.  I have experienced Wind Chill’s in the -40 range before, although back then it was in the -50′s.   I know, I sound like your grandparents telling the story about walking both ways to school in snow, uphill and so on.   I am not making my story sound worse than it was though, the Wind Chill formula has changed about 10 years ago.   There was some exaggeration in the way the old Wind Chill formula worked out.  It did not properly take into account the way the wind and temperature affected human skin.  In fact it was more of a formula based on the thermodynamic properties of water in a jar.   The new Wind Chill formula takes into account wind speed at 5 feet above the ground (the average height of a human face).  It also takes into effect the physical properties of a human face, and how our bodies lose heat during cold weather.   There are some things that are assumed in the formula, like that you are dressed properly.  Clearly, if you were in swimming trunks at 20 below zero, your heat transfer would be rapidly accelerated.  Also, most people wouldn’t go outside in soaking wet clothes when its cold out.  The formula doesn’t count sunlight as having an effect.   Below is the National Weather Service Wind Chill Chart.  Another thing that this new chart shows now is a color coating system to estimate the amount of exposure time needed on bare skin to get frostbite.

If you are one of those that doesn’t quite believe in Wind Chills, think of this.   If you have ever been outside at a restaurant or other setting that has the outdoor heaters, on cool/cold evenings, its pretty tolerable if there no wind, right?   Well that’s because the heaters are transferring heat to the colder air, and since the air isn’t moving it stays warmer in the area close to the heater.  When it’s windy however, it seems like those heaters aren’t working, because they give off so much heat, and the wind just quickly blows it away.   Our bodies work the same way, creating heat, and giving it off to the colder air around us.  If there is lots of wind, it will just keep bringing fresh cold air close to our bodies to constantly heat up.    Remember on cold days to dress in layers, and keep your toes, hands, face and top of your head warm and covered!