Manhattan Project National Historical Park in September
September at Manhattan Project National Historical Park averages a daytime high near 74°F and an overnight low around 49°F, with about 2" of precipitation. Visitation runs about 1.2× the park's average month, which makes September a busy month here.
- Average low
- 49°F
- Average high
- 74°F
Range across the year: 21°F to 83°F
- Precipitation
- 2.0 in
- Daylight
- 12.2 hours
Roughly 10% of the park's yearly visitors come in September: roughly 6,600 recreation visits in a typical year, based on National Park Service monthly counts from 2016 to 2025.
That makes September the 5th-busiest of the park's twelve months, sitting between the July peak (1.7×) and the January low (0.3×).
On our Best Time to Visit score September rates 56/100 ("Fair"). Our recommended month is May: pleasant weather with noticeably thinner crowds (shoulder season).
The daily average of about 62°F is a comfortable range for hiking and being outdoors all day. These figures are 1991–2020 NOAA climate normals from the nearest station, about 1.6 miles from the park.
Because June, July and August together draw about 37% of annual visitors, choosing September instead steps outside that summer crush — the single biggest lever on how crowded the park feels.
You'll have about 12.2 hours of daylight in September to explore — between the 9.6-hour midwinter low and the 14.4-hour summer high.
Park-wide, 2025 drew 56,390 recreation visits, down 24.5% from 74,693 in 2024.
Across the past decade overall visitation has eased about 43.1%, so September may feel a touch quieter than it once did.
How September compares with the months around it
| Month | Avg high / low | Crowds | Best-time score |
|---|---|---|---|
| August | 80°F / 55°F | 1.4× Busy | 59 Fair |
| September | 74°F / 49°F | 1.2× Busy | 56 Fair |
| October | 63°F / 38°F | 1.2× Busy | 39 Poor |
All twelve months at Manhattan Project, with the best time to visit.
Things to do at Manhattan Project in September
The National Park Service tags 54 Manhattan Project activities for fall. Here are 8 of them. Each links to the park's own page for it.
- Alamogordo: Visit the Trinity Site · 1-6 hours
- Los Alamos: Tour Behind the Fence · 4 hours · reservation required
- Hanford: Attend a B Reactor Tour · 4 hours · reservation required
- Hanford: Enjoy a Pre-War Historic Sites Tour · 4 hours · reservation required
- Hanford: Hike the White Bluffs North Trail · 2-4 hours
- Hanford: Join a Ranger Program · 1-3 hours · reservation required
- Hanford: Paddle the Hanford Reach · 4-6 hours
- Los Alamos: Picnic at Ashley Pond · 30-90 minutes
Frequently Asked Questions
September averages a daytime high near 74°F and an overnight low around 49°F at Manhattan Project National Historical Park, with about 2 inches of precipitation. These are 1991–2020 NOAA climate normals from the nearest station, about 1.6 miles from the park, so conditions inside the park can differ, especially at other elevations.
September is busy at Manhattan Project National Historical Park (about 1.2× the average month). Our best-time score rates it "Fair" at 56/100. Our recommended month 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.
A typical September sees about 7,000 recreation visits at Manhattan Project National Historical Park, based on National Park Service monthly counts from 2016–2025.
Where to stay near Manhattan Project in September
Booking a September trip to Manhattan Project National Historical Park? Compare hotels, cabins and vacation rentals near the park with live September availability and prices.
Top-rated places to stay near Manhattan Project
Prices for Oct 30–Nov 1, 4 adults. Change dates on the map below.
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See the full ranking of the best national parks to visit in September.
Source: National Park Service Visitor Use Statistics (2016–2025), NOAA NCEI Climate Normals 1991–2020. Updated 2026-10-11.