14.0 usable nights
12–17 in the middle half of years · 4.8 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 San Diego
August: 23.8 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Bright skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.18.5–19.2 mag/arcsec²
The short answer
August has been strongest.
It averages 23.8 usable nights, versus 11.9 in February. A typical August lands between 23 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
11.9 usable nights
8–15 in the middle half of years · 3.8 typically near a dark moon.
285 astronomical-dark hours in an average month
12.5 usable nights
10–16 in the middle half of years · 3.9 typically near a dark moon.
290 astronomical-dark hours in an average month
13.8 usable nights
13–15 in the middle half of years · 4.0 typically near a dark moon.
240 astronomical-dark hours in an average month
13.3 usable nights
10–17 in the middle half of years · 4.4 typically near a dark moon.
215 astronomical-dark hours in an average month
20.8 usable nights
18–26 in the middle half of years · 6.7 typically near a dark moon.
180 astronomical-dark hours in an average month
21.6 usable nights
19–25 in the middle half of years · 7.0 typically near a dark moon.
197 astronomical-dark hours in an average month
23.8 usable nights
23–25 in the middle half of years · 8.0 typically near a dark moon.
246 astronomical-dark hours in an average month
22.4 usable nights
20–25 in the middle half of years · 7.9 typically near a dark moon.
259 astronomical-dark hours in an average month
20.1 usable nights
18–22 in the middle half of years · 6.9 typically near a dark moon.
310 astronomical-dark hours in an average month
16.4 usable nights
14–18 in the middle half of years · 5.8 typically near a dark moon.
325 astronomical-dark hours in an average month
13.3 usable nights
10–16 in the middle half of years · 5.2 typically near a dark moon.
348 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.