Winter storms are responsible for billion-dollar economic losses in the western US. As storm structures are not well resolved by global climate models, it is not well established how single events and their structures change with warming. Here we use regional storm-resolving simulations to investigate climate change impact on western US winter storms. Under high emissions scenario, precipitation volume from the top 20% of winter storms is projected to increase by up to 40% across the region by the mid-century. The average increase of precipitation volume by 31% is contributed by 22% from increasing area coverage and 19% from increasing storm intensity, while a robust storm sharpening with larger increase in storm center precipitation compared to increase in storm area reduces precipitation volume by 10%. Ignoring the storm sharpening could result in an overestimation of the changes in design storms that are currently used in infrastructure planning in the region.