Mount Vernon, Washington, gets 40 inches of rain per year. The US average is 39. Snowfall is 5 inches. The average US city gets 26 inches of snow per year. The number of days with any measurable precipitation is 95. On average, there are 156 sunny days per year in Mount Vernon, Washington. The July high is around 73 degrees. The January low is 34. Sperling's comfort index for Mount Vernon is a 76 out of 100, where a higher score indicates a more comfortable year-around climate. The US average for the comfort index is 54.