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.

NOAA’s Space Weather Prediction Center has issued a G2 geomagnetic storm watch for July 3 after the sun’s biggest flare of the week triggered radio blackouts across North America.

The Pacific has flipped into its warm phase, and the agency’s new measuring stick says this one could be big. Here is what an El Niño winter usually brings.