13.1 usable nights
11–16 in the middle half of years · 4.5 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 Fallbrook
October: 16.8 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.19.7–20.3 mag/arcsec²
The short answer
October has been strongest.
It averages 16.8 usable nights, versus 7.8 in June. A typical October lands between 14 and 19 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
11.3 usable nights
8–14 in the middle half of years · 3.5 typically near a dark moon.
286 astronomical-dark hours in an average month
10.6 usable nights
6–14 in the middle half of years · 3.0 typically near a dark moon.
289 astronomical-dark hours in an average month
11.3 usable nights
9–14 in the middle half of years · 3.5 typically near a dark moon.
240 astronomical-dark hours in an average month
8.0 usable nights
6–12 in the middle half of years · 2.8 typically near a dark moon.
210 astronomical-dark hours in an average month
7.8 usable nights
6–9 in the middle half of years · 2.2 typically near a dark moon.
180 astronomical-dark hours in an average month
10.9 usable nights
8–14 in the middle half of years · 3.4 typically near a dark moon.
194 astronomical-dark hours in an average month
13.8 usable nights
11–17 in the middle half of years · 4.5 typically near a dark moon.
244 astronomical-dark hours in an average month
16.5 usable nights
14–19 in the middle half of years · 6.2 typically near a dark moon.
258 astronomical-dark hours in an average month
16.8 usable nights
14–19 in the middle half of years · 6.0 typically near a dark moon.
310 astronomical-dark hours in an average month
14.3 usable nights
11–17 in the middle half of years · 5.3 typically near a dark moon.
326 astronomical-dark hours in an average month
11.9 usable nights
7–17 in the middle half of years · 4.2 typically near a dark moon.
351 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.