8.6 usable nights
4–12 in the middle half of years · 2.2 typically near a dark moon.
347 astronomical-dark hours in an average month
20-year trip-planning baseline
Best time to stargaze at Napa
July: 23.6 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.19.6–20.3 mag/arcsec²
The short answer
July has been strongest.
It averages 23.6 usable nights, versus 8.1 in December. A typical July lands between 21 and 27 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
9.3 usable nights
6–11 in the middle half of years · 3.1 typically near a dark moon.
290 astronomical-dark hours in an average month
9.8 usable nights
8–12 in the middle half of years · 2.9 typically near a dark moon.
280 astronomical-dark hours in an average month
13.0 usable nights
11–17 in the middle half of years · 4.3 typically near a dark moon.
236 astronomical-dark hours in an average month
15.4 usable nights
12–18 in the middle half of years · 5.4 typically near a dark moon.
186 astronomical-dark hours in an average month
19.9 usable nights
17–24 in the middle half of years · 6.5 typically near a dark moon.
180 astronomical-dark hours in an average month
23.6 usable nights
21–27 in the middle half of years · 7.4 typically near a dark moon.
186 astronomical-dark hours in an average month
23.6 usable nights
21–27 in the middle half of years · 7.9 typically near a dark moon.
223 astronomical-dark hours in an average month
20.7 usable nights
19–23 in the middle half of years · 7.5 typically near a dark moon.
251 astronomical-dark hours in an average month
18.7 usable nights
17–21 in the middle half of years · 6.3 typically near a dark moon.
308 astronomical-dark hours in an average month
12.6 usable nights
10–14 in the middle half of years · 3.8 typically near a dark moon.
329 astronomical-dark hours in an average month
8.1 usable nights
6–9 in the middle half of years · 2.7 typically near a dark moon.
365 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.