Yellowstone National Park had its third busiest September on record this year with over 640,000 visits. This total is down about 9 percent from September 2016.The 2017 total is also less than the second-busiest September in 2015. Inclement weather might have contributed to the decline in visits last month, according to National Park officials. Snow, ice, and avalanche danger caused several days of road closures throughout September.