12.5 usable nights
10–15 in the middle half of years · 4.4 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 Joshua Tree National Park
June: 22.8 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Threatened dark skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.21.1–21.5 mag/arcsec²
The short answer
June has been strongest.
It averages 22.8 usable nights, versus 12.1 in December. A typical June lands between 20 and 25 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
12.8 usable nights
9–16 in the middle half of years · 4.0 typically near a dark moon.
287 astronomical-dark hours in an average month
13.0 usable nights
9–16 in the middle half of years · 4.2 typically near a dark moon.
288 astronomical-dark hours in an average month
16.1 usable nights
12–21 in the middle half of years · 5.6 typically near a dark moon.
240 astronomical-dark hours in an average month
18.7 usable nights
15–23 in the middle half of years · 5.9 typically near a dark moon.
207 astronomical-dark hours in an average month
22.8 usable nights
20–25 in the middle half of years · 7.5 typically near a dark moon.
180 astronomical-dark hours in an average month
16.7 usable nights
12–20 in the middle half of years · 5.6 typically near a dark moon.
192 astronomical-dark hours in an average month
19.8 usable nights
18–22 in the middle half of years · 5.7 typically near a dark moon.
242 astronomical-dark hours in an average month
21.8 usable nights
19–24 in the middle half of years · 8.3 typically near a dark moon.
257 astronomical-dark hours in an average month
22.1 usable nights
19–25 in the middle half of years · 7.5 typically near a dark moon.
310 astronomical-dark hours in an average month
16.6 usable nights
14–20 in the middle half of years · 5.5 typically near a dark moon.
326 astronomical-dark hours in an average month
12.1 usable nights
10–14 in the middle half of years · 4.2 typically near a dark moon.
354 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.