NWS Wind Chill Chart

About the New Index

On November 1, 2001 the National Weather Service (NWS) implemented a replacement Wind Chill Temperature (WCT) index for the 2001 / 2002 winter season. The reason for the change was to improve upon the current WCT Index used by the NWS and the Meteorological Services of Canada (MSC, the Canadian equivalent of the NWS), which was based on the 1945 Siple and Passel Index.

The new formula makes use of advances in science, technology, and computer modeling to provide a more accurate, understandable, and useful formula for calculating the dangers from winter winds and freezing temperatures. In addition, clinical trials have been conducted and the results have been used to verify and improve the accuracy of the new formula.

New Index Goals

Standardization of the WCT Index among the meteorological community is important, so that an accurate and consistent measure is provided and public safety is ensured.

The goal was to implement the new wind chill formula in Canada and the United States during the same time frame in order to have a consistent WCT Index for North America.