The 2 largest cities in Idaho are Boise with a population of  145,987 and Nampa with 81,557. The next 3 largest cities are  Meridian with 75,092, Idaho Falls with 56,813 and â¦ Pocatello with  54,255.
Averages for Washington DC in September. The weather in September in Washington DC is very attractive for those that want to avoid the peak heat of summer, yet still enjoy lots of warm days on their visit. On average, peak temperatures during the day in September still reach up to 27Â°C.
Average Weather in September in Seattle Washington, United States. In Seattle, the month of September is characterized by falling daily high temperatures, with daily highs decreasing by 8Â°F, from 75Â°F to 67Â°F over the course of the month, and rarely exceeding 83Â°F or dropping below 60Â°F.