How Crowded Is Manhattan Project in September?
September is a busy month at Manhattan Project National Historical Park, running about 1.2× the park's average month — roughly 10% of the year's visitors come in September. That puts it between the July peak and the January low. Overall our best-time score rates September as "Fair" for a visit. Typical September weather averages a high near 74°F and a low around 49°F, with about 2" of precipitation. You'll get about 12.2 hours of daylight to explore.
Frequently Asked Questions
September is busy at Manhattan Project National Historical Park (about 1.2× the average month). Our best-time score rates it "Fair". The single best month overall is May.
The busiest month is July and the quietest is January. September sits at about 1.2× the park's average, or 10% of annual visitation.
Source: National Park Service Visitor Use Statistics (2016–2025), NOAA NCEI Climate Normals 1991–2020. Updated 2026-06-20.