A central AC running flat out at 79 degrees on a 99-degree afternoon is usually doing exactly what it was engineered to do. The symptom that actually signals a fault is different, and easy to miss.

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.

More than 165 million Americans face major or extreme heat risk this week as a record-threatening heat dome settles over the East Coast and Midwest through the July Fourth weekend — and complicates World Cup matches.

A heat-stressed transformer failure in Brittany cut power to tens of thousands of homes as France logged its hottest day on record and Europe's heatwave spread north.

Forty people have drowned trying to cool off, two small children died in a hot car, and France just recorded its warmest night on record. The heat is now a body count, not a forecast.

Spain braces for 44C, France curbs festival drinking and Britain faces its hottest June day on record as the heat builds toward a Monday peak.