Seeing the Milky Way takes four things at once: a fully dark sky, the galactic core above the horizon, no moon in the sky, and no clouds in the way. Most forecasts give you one of them. This one lines all four up, hour by hour, for the next seven nights.

The ribbon under each verdict is the whole night from 6 pm to 7 am. The blue fades as twilight ends, the pale wash is moonlight, the dotted texture is cloud, and the lilac bar is when the core is up in a dark sky — the window worth driving for.

When the week is a no, the forecast looks further ahead with the moon alone and tells you when the next run of moon-free evenings starts, so you can plan the trip.