3.4 usable nights
2–5 in the middle half of years · 0.9 typically near a dark moon.
359 astronomical-dark hours in an average month
20-year trip-planning baseline
Best time to stargaze at Williston
August: 10.1 usable nights on average. Use this seasonal climate baseline to choose a month, then use the live forecast to choose a night.
Site darkness · modelled, not measured
Bright skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.19.2–19.9 mag/arcsec²
The short answer
August has been strongest.
It averages 10.1 usable nights, versus 0.0 in June. A typical August lands between 9 and 11 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
4.0 usable nights
2–6 in the middle half of years · 1.1 typically near a dark moon.
293 astronomical-dark hours in an average month
2.8 usable nights
1–3 in the middle half of years · 0.8 typically near a dark moon.
264 astronomical-dark hours in an average month
4.9 usable nights
3–6 in the middle half of years · 1.6 typically near a dark moon.
194 astronomical-dark hours in an average month
5.5 usable nights
3–7 in the middle half of years · 2.4 typically near a dark moon.
114 astronomical-dark hours in an average month
0.0 usable nights
0–0 in the middle half of years · 0.0 typically near a dark moon.
60 astronomical-dark hours in an average month
5.5 usable nights
4–6 in the middle half of years · 1.8 typically near a dark moon.
89 astronomical-dark hours in an average month
10.1 usable nights
9–11 in the middle half of years · 3.5 typically near a dark moon.
168 astronomical-dark hours in an average month
10.1 usable nights
8–12 in the middle half of years · 3.6 typically near a dark moon.
236 astronomical-dark hours in an average month
5.3 usable nights
3–7 in the middle half of years · 1.8 typically near a dark moon.
301 astronomical-dark hours in an average month
3.1 usable nights
1–4 in the middle half of years · 1.3 typically near a dark moon.
336 astronomical-dark hours in an average month
2.6 usable nights
1–4 in the middle half of years · 0.7 typically near a dark moon.
372 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.