7.7 usable nights
5–12 in the middle half of years · 2.2 typically near a dark moon.
343 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Porterville
August: 25.1 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Brightened skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.20.2–20.8 mag/arcsec²
The short answer
August has been strongest.
It averages 25.1 usable nights, versus 7.5 in February. A typical August lands between 23 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
7.5 usable nights
3–12 in the middle half of years · 2.1 typically near a dark moon.
288 astronomical-dark hours in an average month
8.3 usable nights
5–12 in the middle half of years · 2.1 typically near a dark moon.
284 astronomical-dark hours in an average month
12.2 usable nights
10–15 in the middle half of years · 3.9 typically near a dark moon.
240 astronomical-dark hours in an average month
16.8 usable nights
13–22 in the middle half of years · 5.8 typically near a dark moon.
194 astronomical-dark hours in an average month
22.8 usable nights
19–27 in the middle half of years · 8.2 typically near a dark moon.
180 astronomical-dark hours in an average month
22.9 usable nights
20–26 in the middle half of years · 7.2 typically near a dark moon.
186 astronomical-dark hours in an average month
25.1 usable nights
23–27 in the middle half of years · 8.3 typically near a dark moon.
235 astronomical-dark hours in an average month
23.6 usable nights
22–25 in the middle half of years · 8.2 typically near a dark moon.
253 astronomical-dark hours in an average month
20.9 usable nights
21–23 in the middle half of years · 7.2 typically near a dark moon.
310 astronomical-dark hours in an average month
13.7 usable nights
11–16 in the middle half of years · 4.3 typically near a dark moon.
328 astronomical-dark hours in an average month
7.8 usable nights
5–11 in the middle half of years · 2.6 typically near a dark moon.
361 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.