Cities don't just run hotter than the countryside — they stay hotter after dark, and the nighttime gap is often wider than the daytime one.

A heat dome is the stalled high-pressure lid behind record-breaking heat waves. Here is how it forms, why humidity makes it deadly, and how long it lasts.

A heat dome has settled over Western Europe for the summer solstice, with France warning Monday could be its hottest day on record and 53 departments already under an orange alert.