8.8 usable nights
6–11 in the middle half of years · 2.6 typically near a dark moon.
348 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Arches National Park
October: 16.6 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Natural-dark skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.21.8–21.9 mag/arcsec²
The short answer
October has been strongest.
It averages 16.6 usable nights, versus 7.7 in March. A typical October lands between 14 and 19 usable nights.
Record2005–2024 · 20 complete years
Usable nightAt least 3 astronomical-dark hours and NASA POWER nighttime cloud ≤30%
Dark-moon nightUsable night with ≤25% illumination at local solar midnight
ResolutionCERES SYN1deg 1° cloud grid; regional climate, not a campsite guarantee
Seasonal fingerprint
Usable nights by month
Month by month
8.3 usable nights
6–11 in the middle half of years · 2.8 typically near a dark moon.
290 astronomical-dark hours in an average month
7.7 usable nights
6–11 in the middle half of years · 2.0 typically near a dark moon.
279 astronomical-dark hours in an average month
9.6 usable nights
9–12 in the middle half of years · 2.6 typically near a dark moon.
234 astronomical-dark hours in an average month
10.1 usable nights
8–12 in the middle half of years · 3.1 typically near a dark moon.
186 astronomical-dark hours in an average month
14.1 usable nights
11–18 in the middle half of years · 4.5 typically near a dark moon.
180 astronomical-dark hours in an average month
8.4 usable nights
5–12 in the middle half of years · 2.7 typically near a dark moon.
186 astronomical-dark hours in an average month
10.2 usable nights
8–12 in the middle half of years · 3.4 typically near a dark moon.
221 astronomical-dark hours in an average month
16.4 usable nights
14–18 in the middle half of years · 5.8 typically near a dark moon.
250 astronomical-dark hours in an average month
16.6 usable nights
14–19 in the middle half of years · 5.4 typically near a dark moon.
308 astronomical-dark hours in an average month
12.6 usable nights
11–15 in the middle half of years · 4.2 typically near a dark moon.
329 astronomical-dark hours in an average month
8.7 usable nights
6–12 in the middle half of years · 2.7 typically near a dark moon.
366 astronomical-dark hours in an average month
Use the baseline honestly
Climate chooses the month. Forecasts choose the night.
The cloud product is a roughly 1° regional grid. It can reveal seasonality, but it cannot know a mountain ridge, valley fog pocket, locked gate, smoke event or the exact sky you will get.
Source: NASA POWER daily data, parameter CLOUD_AMT_NIGHT from the CERES SYN1deg cloud product. GoodSeeing calculates astronomical darkness and lunar illumination independently for each place.