The mercury didn't give a true representation of the temperature yesterday in Sydney with wind chill making it feel significantly colder. At 3:30pm, the temperature at Sydney Airport read 19.7 degrees, however gusty southerly winds exceeding 55 km/h and relative humidity of just 50% made it feel like 11.1 degrees. This 9 degree discrepancy between temperatures is commonly known as wind chill and becomes much more prevalent as the autumn and winter months take hold. As mammals, we generate body warmth which is insulated by our clothes and hair. On gusty days, this thin layer of body warmth is disturbed and we feel cooler. Usually the amount of moisture in the air is more noticeable on warmer days. High humidity will often make a 35 degree day feel closer to 40 degrees as our coping mechanism (sweating) is less effective. Sweating allows mammals to cool off via evaporative cooling, however if the air is already saturated, sweating becomes less effective. This phenomenon is called heat stress. Conversely, on a day where the relative humidity is low, there is more potential for moisture loss and our cooling mechanism becomes much more effective. As a result, the days which are cool, gusty and dry, we tend to feel the impacts of wind chill. Southerly winds have continued to blow throughout today, however not strong and with more moisture in the air. As a result, there has only been a 4-5 degree discrepancy between the actual temperature and the 'feels like' temperature.