The contrast distortions are weighted according to their individual visibilities approximated by the HVS. High winds caused near zero visibilities and treacherous travel conditions in many areas. The intensity interferometer measures interferometric visibilities like all other astronomical interferometers. On the 26th, visibilities in some towns were less than 0.1 miles. As a result, visibilities in thundersnow are frequently under 2/5th of a mile. A blizzard tends to reduce visibilities to 1/4 of a mile (400 m) or less. Snowfall of this intensity may limit visibilities severely, even during light wind conditions.