This study proposes parameters to measure the effect of snow cover on the threshold wind velocity of dust outbreak for dust models. We used statistics of snow cover, wind velocity and dust outbreaks in East Asia for the months of March and April for the years from 1988 to 2003. Dust events frequently occur in that region in those months, although snow and melting snow cover a broad area, making it difficult to know the distribution of dust from East Asia. Our equation, presented in this paper, shows the degree to which snow cover affects dust outbreaks. To validate this equation, we checked the correlation between frequency of strong winds and dust outbreaks. Our results showed that this correlation is improved when the effect of snow cover is considered. We discuss the effects of soil wetness, vegetation, and errors due to the subgrid heterogeneity of snow coverage as well.