In recent years, flood damage in urban areas due to localized heavy rain has been a serious problem. In order to save life from the flood damage, rainfall forecast is important even if 10-minute lead time. To improve the rainfall forecast system, an index is necessary to detect the hazardous storm.
 High Z_DR area which is extending above the freezing level, i.e. a Z_DR column, is associated with strong updraft. We investigated a relation between the Z_DR column and storm development using X-band polarimetric radar observations. It is known that Z_DR is susceptible from rainfall attenuation especially in X-band radar. On the other hand, K_DP is not affected from rainfall attenuation. Therefore, we also studied the effectiveness of K_DP column. We found that Z_DR column (K_DP column) were formed about 15 min (10 min) prior to the onset of heavy rainfall on the ground based on the cell tracking algorithm.