The convert([t, s], windchill, [ut, us]) function converts the temperature-speed pair  to the corresponding windchill factor corresponding to the units of temperature ut.

The convert([t*Unit(ut), s*Unit(us)], windchill ) function is similar to the first calling sequence.

The formula used by the National Weather Service is

where T is the temperature in degrees Fahrenheit, and V is the wind velocity in miles per hour.  The result is the apparent temperature in degrees Fahrenheit.

This calculation is intended as an approximation. It is used only for wind speeds between 4 mph (  ) and 50 mph (  ).