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What a 'super El Niño' could mean for winter in 7 U.S. regions

A super El Niño winter tends to bring wetter weather to the southern U.S. and milder conditions up north, though no state's winter is guaranteed

A patch of unusually warm water in the tropical Pacific can shift the odds for a soggy winter in Los Angeles. The same patch can tilt Minneapolis toward a thin snow season, thousands of miles from where the warming starts. That reach is why seasonal forecasters watch the Pacific so closely.

El Niño is a warming of surface water in the central and eastern tropical Pacific. It is the warm phase of the El Niño–Southern Oscillation, or ENSO. NOAA's Climate Prediction Center declares El Niño conditions when sea surface temperatures in a stretch of ocean known as the Niño-3.4 region run at least 0.5°C above average. The agency must also expect that warmth to persist.

A 'super El Niño' is a stronger version of the same event. The phrase is an informal media label for an unusually strong El Niño, and NOAA has no official category by that name. Usage varies, so the term has no single agreed threshold. The strong El Niño winters most often cited as benchmarks are 1982–83, 1997–98 and 2015–16.

A strong El Niño tends to push the Pacific jet stream farther south and make it stronger across North America. In a super El Niño winter, that shift typically leaves the southern U.S. wetter than average and the northern tier warmer than average. That broad split hides real regional differences. Heavier rain and flood risk in California, cooler and wetter weather along the Gulf Coast and strain on snowpack in the Pacific Northwest all trace back to the same shift.

The slides that follow group states into seven regions, from California and the Southwest to the Northeast and mid-Atlantic. Three more slides explain what the term means, how the jet stream moves and why the pattern can fail to show up. The list does not cover every state individually. Each slide describes what strong El Niño winters have tended to bring, not a forecast for any particular year.

Seasonal outlooks shift the odds for an entire season. They do not predict individual storms. Any single winter can also break from the typical pattern. Other large-scale atmospheric patterns can override the El Niño signal in a given year.

What a super El Niño is

A super El Niño is an informal label for an unusually strong El Niño, the periodic warming of surface water in the central and eastern tropical Pacific. NOAA has no official "super" category. The term describes intensity rather than a separate kind of event.

El Niño is the warm phase of a natural climate cycle called the El Niño–Southern Oscillation, or ENSO. The cycle swings between that warm phase, a cool phase known as La Niña and a neutral state in between. Episodes recur irregularly, typically every two to seven years.

The name has two parts. El Niño refers to the ocean side. Peruvian fishermen used the Spanish phrase for "the little boy," a reference to the Christ child, for warm coastal water that often arrived around Christmas. The Southern Oscillation refers to the atmosphere, a seesaw in air pressure between the eastern and western tropical Pacific.

During El Niño, the trade winds that normally push warm water west across the Pacific weaken. Warm water spreads east, and the zone of heavy tropical rainfall shifts with it. That change in where heat and moisture enter the atmosphere is how ocean temperatures near the equator end up affecting weather far from the Pacific.

NOAA's Climate Prediction Center measures events with the Oceanic Niño Index. The index is a three-month running average of sea surface temperature departures from normal in the Niño-3.4 region. A typical El Niño clears the agency's minimum warming threshold. Super El Niño is the phrase news outlets and some forecasters use when the warming runs far beyond that minimum.

Usage of the label varies from one outlet to the next. No single official temperature cutoff separates a super event from a strong one. NOAA does not publish a dividing line between the two.

Timing explains why the strength of an event gets so much attention ahead of winter. ENSO events typically reach peak strength in the Northern Hemisphere's late fall or winter. The strongest past events serve as reference points. Each of those winters played out differently across the U.S., and none sets a formula for the next one.

How El Niño shifts the winter jet stream

A strong El Niño tends to pull the Pacific jet stream farther south and make it stronger as it crosses North America. That shift steers more storms into the southern U.S. and leaves the northern tier warmer than average.

The jet stream is a narrow band of fast wind high in the atmosphere, near the cruising altitude of commercial airliners. It flows from west to east. Winter storms tend to form along it and follow its path. Where the jet sits helps decide which regions get rain and snow.

During El Niño, unusually warm water in the central and eastern tropical Pacific heats the air above it. That warm, moist air rises and builds towering clusters of thunderstorms farther east than usual. The heat released by those storms high in the atmosphere alters wind patterns far beyond the tropics.

Over North America, the result is an extended, energized Pacific jet that often stretches across the southern U.S. Storm systems ride that jet from the Pacific toward the southern states. This is the main reason the southern tier of the U.S. leans wetter........

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