6.0 usable nights
3–8 in the middle half of years · 2.0 typically near a dark moon.
344 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Hanford
August: 26.0 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.19.9–20.5 mag/arcsec²
The short answer
August has been strongest.
It averages 26.0 usable nights, versus 6.0 in January. A typical August lands between 24 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
9.8 usable nights
7–12 in the middle half of years · 3.3 typically near a dark moon.
289 astronomical-dark hours in an average month
11.1 usable nights
8–13 in the middle half of years · 2.6 typically near a dark moon.
283 astronomical-dark hours in an average month
16.4 usable nights
14–18 in the middle half of years · 5.5 typically near a dark moon.
240 astronomical-dark hours in an average month
20.9 usable nights
18–23 in the middle half of years · 7.1 typically near a dark moon.
192 astronomical-dark hours in an average month
23.6 usable nights
20–27 in the middle half of years · 8.3 typically near a dark moon.
180 astronomical-dark hours in an average month
24.6 usable nights
21–28 in the middle half of years · 7.8 typically near a dark moon.
186 astronomical-dark hours in an average month
26.0 usable nights
24–27 in the middle half of years · 8.3 typically near a dark moon.
233 astronomical-dark hours in an average month
23.4 usable nights
22–25 in the middle half of years · 8.3 typically near a dark moon.
253 astronomical-dark hours in an average month
19.2 usable nights
15–23 in the middle half of years · 6.6 typically near a dark moon.
310 astronomical-dark hours in an average month
11.3 usable nights
9–14 in the middle half of years · 3.8 typically near a dark moon.
328 astronomical-dark hours in an average month
6.8 usable nights
3–11 in the middle half of years · 2.5 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.