The development and validation of a method to estimate visibility during snowfall and blowing snow

Information on the occurrence of blowing snow enables drivers to reroute or reschedule their trips to avoid encountering severe snowstorm conditions. Such information also is necessary to enable traffic management personnel to properly exercise traffic control measures. Visibility meters are used to measure the intensity of blowing snow on roads. However, the area covered by presently installed visibility meters is too limited to obtain region-wide information on blowing snow. We seek methods of estimating the intensity of blowing snow using wind velocity and snowfall intensity, both of which are obtained relatively easily. First, based on past studies on mass flux of snow (Mf) and visibility (Vis), we find that Vis=10^(−0.773×log(N×V)+2.85) for visibilities up to 3000 m. Considering that mass flux of snow equates to concentration of suspended snow particle multiplied by wind velocity, we then derive a method to estimate concentration of suspended snow particle from wind velocity and snowfall intensity. To verify the accuracy of the estimation method, we compare the estimated visibility with measured visibility. We divide visibility values into five ranks: <100, 100-200, 200-500, 500-1000, and >=1000 m. This gives us 5×5 contingency tables. The verification finds a percent correct of 79% when calculated using hourly value, and 71% when calculated using 10-min value. We conclude that this method is appropriate for estimating current and future reduced visibility toward improved winter road safety.