12.6 usable nights
11–16 in the middle half of years · 4.3 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 Sylmar
August: 27.0 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Bright urban skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.18.3–19.1 mag/arcsec²
The short answer
August has been strongest.
It averages 27.0 usable nights, versus 12.4 in March. A typical August lands between 25 and 28 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
13.0 usable nights
9–18 in the middle half of years · 4.3 typically near a dark moon.
287 astronomical-dark hours in an average month
12.4 usable nights
9–16 in the middle half of years · 3.5 typically near a dark moon.
287 astronomical-dark hours in an average month
15.8 usable nights
14–17 in the middle half of years · 5.3 typically near a dark moon.
240 astronomical-dark hours in an average month
19.1 usable nights
16–22 in the middle half of years · 6.3 typically near a dark moon.
204 astronomical-dark hours in an average month
22.6 usable nights
19–26 in the middle half of years · 7.5 typically near a dark moon.
180 astronomical-dark hours in an average month
24.6 usable nights
22–27 in the middle half of years · 8.0 typically near a dark moon.
190 astronomical-dark hours in an average month
27.0 usable nights
25–28 in the middle half of years · 9.1 typically near a dark moon.
241 astronomical-dark hours in an average month
24.3 usable nights
23–26 in the middle half of years · 8.7 typically near a dark moon.
256 astronomical-dark hours in an average month
22.0 usable nights
19–25 in the middle half of years · 7.8 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 · 6.0 typically near a dark moon.
326 astronomical-dark hours in an average month
13.0 usable nights
9–18 in the middle half of years · 4.8 typically near a dark moon.
356 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.