New Wind Chill Chart
This winter, the National
Weather Service and Meteorological Services of Canada will use the following Wind
Chill Temperature Index, designed to calculate a more accurate reading of how
the cold air feels on the human skin.
Since 1945, the United States and Canada have used an index, which relied on
observed winds 33 feet above the ground, and focused on how fast the cold
temperatures combined with winds made water freeze. The new index accounts for
the wind effects at face level, and a better calculation for body heat loss.
For example, under the old index system, a temperature of 20 degrees, with a 15
mph wind, translated into a reading of five degrees below zero. The new index
calculation would translate the same conditions to six degrees above zero.
The new index is based on:
- Wind speed calculated at the average height of the human face,
about five feet (the human face is most often exposed to the cold).
- Updated heat transfer theory, which factors heat loss from the body
to its surroundings during cold, windy days.
- A consistent standard for skin tissue resistance.
- Clear night sky conditions.
- A lowered calm wind threshold from four mph to three mph.
Further Information:
NWS Office of Climate, Water
and Weather Services, which includes the chart and wind chill calculator
that appear above.