Two opposite moods of the same ocean decide your winter. One of them is building toward record strength right now — and it flips all nine of these.
El Niño spreads warm water east across the tropical Pacific. La Niña does the reverse, letting cold water surface. Half a degree either way is enough to start it.
Trade winds normally push Pacific surface water west. El Niño weakens them, so warm water sloshes back east. La Niña strengthens them and piles it west again.
Warm Pacific water drags the jet stream south of its usual line in El Niño years. La Niña shoves it north. Everything downstream follows that one shift.
A southward jet steers storm after storm into the southern states. El Niño winters run wet there; La Niña winters tend to leave the same states in drought.
With the jet pushed south, the northern tier and Pacific Northwest turn drier and milder. La Niña does the opposite: soaking rain and deep snow up north.
El Niño lifts high-level winds over the Atlantic, shearing the tops off young storms. Fewer Atlantic hurricanes, more in the eastern Pacific. La Niña flips it.
The warm water that soaks the Americas starves Australia and Indonesia of rain, driving drought and fire risk. La Niña sends those same regions flooding.
Warm water caps the cold upwelling off Peru and the anchovy shoals collapse. Fishermen named the pattern El Niño because it tended to arrive near Christmas.
El Niño moves stored ocean heat into the air, so its years top the global temperature charts. La Niña buries that heat again and briefly cools the average.
Forecasters put the odds of a very strong El Niño across October to December at 95%, with a 69% chance it outruns every event on record going back to 1950.