Kosa is less likely to originate in the winter when rain falls little and the land surface becomes dry, because the weather during that season stays mild with no strong wind, due to the Siberian high pressure, and in addition, the surfaces of almost all of the dry areas are covered with snow.
降水量が少なく地面が乾燥する冬は、シベリア高気圧の影響で風があまり強くない穏やかな天候が続くうえ、ほとんどの乾燥地帯の表土は積雪に覆われてしまうため、黄砂が発生しにくい。