fuagf -- at -40°F, only takes a 15 mph wind for a wind chill of -70°F -- so if you did see -40°F, likely you also saw the -70°F wind chill http://www.nws.noaa.gov/om/cold/cold-images/windchill.gif http://www.nws.noaa.gov/om/cold/wind_chill.shtml when I was in Chicago when it hit that record -27°F, the wind was gusting to 55 to 60 mph -- so that was good for a wind chill of about -70°F