2.1 usable nights
1–4 in the middle half of years · 0.8 typically near a dark moon.
356 astronomical-dark hours in an average month
20-year trip-planning baseline
Best time to stargaze at Green Bay
September: 6.7 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.18.8–19.5 mag/arcsec²
The short answer
September has been strongest.
It averages 6.7 usable nights, versus 0.8 in May. A typical September lands between 4 and 9 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
1.9 usable nights
1–2 in the middle half of years · 0.6 typically near a dark moon.
292 astronomical-dark hours in an average month
2.7 usable nights
1–4 in the middle half of years · 0.8 typically near a dark moon.
270 astronomical-dark hours in an average month
1.9 usable nights
1–3 in the middle half of years · 0.6 typically near a dark moon.
208 astronomical-dark hours in an average month
0.8 usable nights
0–0 in the middle half of years · 0.3 typically near a dark moon.
152 astronomical-dark hours in an average month
1.3 usable nights
0–1 in the middle half of years · 0.6 typically near a dark moon.
120 astronomical-dark hours in an average month
2.6 usable nights
0–4 in the middle half of years · 0.6 typically near a dark moon.
131 astronomical-dark hours in an average month
3.7 usable nights
0–6 in the middle half of years · 1.2 typically near a dark moon.
194 astronomical-dark hours in an average month
6.7 usable nights
4–9 in the middle half of years · 2.4 typically near a dark moon.
245 astronomical-dark hours in an average month
4.5 usable nights
2–6 in the middle half of years · 1.6 typically near a dark moon.
303 astronomical-dark hours in an average month
3.2 usable nights
1–4 in the middle half of years · 1.0 typically near a dark moon.
332 astronomical-dark hours in an average month
1.6 usable nights
1–2 in the middle half of years · 0.5 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.