Teleconnections

A warm stripe of water at the equator should not, on the face of it, decide whether it rains in Los Angeles or Nairobi. Teleconnections are the reason it does: the atmosphere's long-distance transmission lines, carrying the tropical Pacific's disruption to weather patterns continents away.

The mechanism starts with rainfall, not temperature. El Niño moves the tropics' most powerful thunderstorm clusters east into the central Pacific; those storms pump enormous heat into the upper atmosphere at a new longitude. The displaced heating launches Rossby waves — planetary-scale undulations — that arc through the jet streams of both hemispheres, strengthening some (the winter subtropical jet across the southern United States is the classic case), shifting others, and parking ridges and troughs in preferred positions for a season.

Each downstream tilt in our impacts guides is a teleconnection: the stormy US southern tier, the dry Australian spring, East Africa's loaded short rains, the sheared-apart Atlantic hurricane season. Two properties matter for reading them honestly. They are probabilistic — preferred patterns, not guarantees, as 2015-16's California proved. And they are strength-sensitive — strong events, like the one tracked on the dashboard, produce far more reliable teleconnections than weak ones.