Clear skies over San Mateo, CA tonight

San Mateo ranks 332nd out of 500 US cities for night-sky darkness, with a darkness index of 61 out of 100. That estimate comes from the population of every community within 150 km, weighted by distance — so what matters is the glow of the whole metro area, not just the city's own size.

That is a bright sky. From the city core expect the Moon, planets and a few dozen of the brightest stars; the Milky Way will not show. Getting out from under the metro's glow is the single biggest improvement available to you.

If you are willing to drive, Napa, CA sits under noticeably darker sky and is the nearest city on our ranking with a real improvement. Give your eyes about 20 minutes to adapt once you arrive, and avoid looking at your phone.

Light pollution is the part that does not change night to night. Cloud cover and moonlight do, which is what the forecast above tracks.