Ohio Winter Safety Week 2009

The New Wind Chill Index

Photo copyright University Corporation for Atmospheric Research. Used with permission.

The National Weather Service and the Meteorological Services of Canada have designed a Wind Chill Temperature Index designed to calculate a more accurate reading of how the cold air feels on human skin.

Since 1945, the United States and Canada hace used an index which relied on pbserved 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 -5 degrees. The new index calculation would translate the same conditions to 6 degrees above zero.

The new index is based on:

• Wind speed calculated at the average height of the human face, or about 5 feet. The human face is the most often exposed part of the human body.
• Updated heat transfer theory which factors heat loss from the body to its surroundings during cold, windy days.
• A consistant standard for skin tissue resistance.
• Clear night sky conditions
• A lowered calm wind speed threshold from four miles to three miles.

To obtain more information on the wind chill change, visit the National Weather Service at http://www.nws.noaa.gov/om/winter/index.shtml.

Thanks to Gary Garnet, Warning and Coordination Meteorologist at the National Weather Service, Cleveland.