Many conifers suffer from desiccation of shoots in winter rather than from direct thermal damage. When the injury is severe, all the needles and buds are killed. Usually, however, the buds escape severe damage. Damage always occurs when water loss through transpiration is greater than water uptake. Bright, warm sunny winter days, especially if they are windy, the temperature above freezing, and the soil frozen, increase the vapor pressure gradient between leaves and the air, causing water to be lost at a high rate.
Wind exacerbates the problem.
In simple terms, the leaves lose water faster than they can take it up under our dry conditions. Even if the soil is partially thawed but air temperatures are only a few degrees below freezing, water in the xylem remains frozen and the plant cannot transport water into the leaves. Some extracellular freezing also occurs in the plant where water is pulled out of the cells and collects as ice in the intercellular spaces. Occasionally, the whole tree is discolored. Usually, damage is most severe on the south and southwest sides of the trees, with much variation among species.