by using Canada's new Wind Chill formula and Chart @
http://www.theweathernetwork.com/int...windchill4.htm
wind chill temp, WCT = 13.12 + 0.6215 x Tair - 11.37 x V10metre^0.16 +0.3965 x Tair x V10metre^0.16
Where : Tair - is the surface temp in C
V10metre - is the standard surface wind speed in km/hr
so with Tair = -27'C and wind speed = 30km/hr
WCT = -41.6979'C