It is considered that kosa occurs more frequently in spring by the following conditions: Melting snow on the topsoil, being stronger westerlies by weaker high pressures, increasing windy days by passing of developing low pressure, and so on.
春になると、表土を覆った積雪が融け、高気圧の勢力が弱まる代わりに偏西風が強まり、低気圧が発達しながら通過するなどして風が強い日が増えるため、黄砂の発生も増えると考えられている。