9.3 usable nights
7–12 in the middle half of years · 2.5 typically near a dark moon.
341 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Flagstaff
October: 20.0 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Brightened skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.20.1–20.7 mag/arcsec²
The short answer
October has been strongest.
It averages 20.0 usable nights, versus 8.4 in July. A typical October lands between 17 and 24 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
10.6 usable nights
7–14 in the middle half of years · 3.0 typically near a dark moon.
288 astronomical-dark hours in an average month
11.6 usable nights
10–14 in the middle half of years · 3.5 typically near a dark moon.
285 astronomical-dark hours in an average month
14.4 usable nights
11–17 in the middle half of years · 4.0 typically near a dark moon.
240 astronomical-dark hours in an average month
16.9 usable nights
14–20 in the middle half of years · 5.7 typically near a dark moon.
199 astronomical-dark hours in an average month
18.4 usable nights
15–22 in the middle half of years · 6.2 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 · 2.9 typically near a dark moon.
187 astronomical-dark hours in an average month
11.5 usable nights
9–14 in the middle half of years · 3.1 typically near a dark moon.
239 astronomical-dark hours in an average month
17.7 usable nights
15–18 in the middle half of years · 6.0 typically near a dark moon.
254 astronomical-dark hours in an average month
20.0 usable nights
17–24 in the middle half of years · 7.0 typically near a dark moon.
310 astronomical-dark hours in an average month
15.7 usable nights
14–17 in the middle half of years · 5.4 typically near a dark moon.
327 astronomical-dark hours in an average month
9.9 usable nights
6–12 in the middle half of years · 3.6 typically near a dark moon.
359 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.