El Niño and La Niña
Also called: ENSO, El Niño-Southern Oscillation
El Niño and La Niña are the warm and cool phases of a recurring climate pattern in the tropical Pacific called the El Niño-Southern Oscillation (ENSO). During El Niño, the trade winds weaken and the central and eastern tropical Pacific runs warmer than average. During La Niña, the trade winds strengthen and the same waters run cooler. Both shift weather patterns worldwide.
Typical Effects on U.S. Winter Weather
| Phase | Southern United States | Northern United States |
|---|---|---|
| El Niño | Wetter than usual, with more flooding along the Gulf Coast and in the Southeast | Warmer and drier than usual |
| La Niña | Warmer and drier than usual, with drought more likely | Wetter and colder than usual, extending into Canada |
These are tendencies across many events. An individual winter can differ.
Source: NOAA National Ocean Service: What Are El Niño and La Niña?
Key Points
- Each phase returns every two to seven years on average, but not on a regular schedule. El Niño is more frequent than La Niña.
- An episode typically lasts nine to 12 months, and some last for years.
- When neither is in place, conditions are called ENSO-neutral, and tropical Pacific temperatures are generally close to average.
- El Niño means Little Boy in Spanish and La Niña means Little Girl.
Related Terms
Jet Stream
A jet stream is a relatively narrow band of strong wind in the upper atmosphere, typically around 30,000 feet, that blows from west to east. The polar jet sits between 50° and 60° latitude and the subtropical jet near 30°. Jet streams follow the boundaries between cold and warm air and steer the storm systems below them.
Atmospheric River
An atmospheric river is a long, narrow corridor of concentrated water vapor moving through the lower atmosphere, typically 250 to 375 miles wide and often more than 1,000 miles long. When one comes ashore and is lifted over mountains, it produces prolonged heavy rain and snow. Atmospheric rivers are rated from AR 1 (weak) to AR 5 (exceptional) by strength and duration.
Pineapple Express
A strong atmospheric river that carries moisture from the tropical Pacific near Hawaii to the West Coast of North America. Because the air is warm, a Pineapple Express raises mountain snow levels, so more precipitation falls as rain and can melt existing snowpack, increasing the flood risk.
Polar Vortex
The polar vortex is a large area of low pressure and cold air surrounding each of Earth's poles. It always exists, weakening in summer and strengthening in winter. During Northern Hemisphere winter it often expands, sending Arctic air south with the jet stream and producing cold outbreaks across the United States.
Hurricane
A tropical cyclone with maximum one-minute sustained surface winds of 74 mph or greater in the Atlantic or eastern and central North Pacific. Hurricanes are categorized 1-5 on the Saffir-Simpson Hurricane Wind Scale, with Category 5 beginning at 157 mph.
El Niño and La Niña: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
In-depth guide
El Niño 2026: How Strong It Is, and What It Actually Means
El Niño is strengthening in 2026, with NOAA calling a strong-to-very-strong event likely through winter and 83% odds of a historic peak that exceeds every event since 1950. What that means for hurricane season and winter.
Weather Education
What Is an Atmospheric River? The AR Scale, the Pineapple Express, and El Niño
Learn what an atmospheric river is, how the AR 1 to 5 scale works, what a Pineapple Express is, and whether a very strong El Niño means more of them for the West Coast this winter.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Guide
Hurricane Categories Explained
Understand what each Saffir-Simpson category says and what it does not say about a storm's risk.
Seasonal Hub
Hurricane Season Guide
Track tropical risk, categories, and preparedness advice in one place.
Feature
Hurricane Tracker
Track cones, watches, warnings, and tropical systems from formation through landfall.
Guide
The Hurricane Cone of Uncertainty
What the cone really means, why impacts reach far outside it, and how to read spaghetti models.
Sources
Explore Other Terms
Storm Surge
Storm surge is an abnormal rise in sea level during a hurricane or other intense storm, measured as the height of the water above the normal predicted tide. It is produced mainly by the storm's winds pushing water toward the shore. Storm surge is the leading cause of deaths from hurricanes.
Nor'easter
A storm along the East Coast with winds blowing from the northeast. Nor'easters can bring heavy snow, rain, and coastal flooding, especially from Virginia to New England. The most powerful nor'easters rival hurricanes in intensity.
King Tide
King tide is a popular, non-scientific name for an exceptionally high tide. King tides happen when the higher tides around a new or full moon coincide with the Moon's closest approach to Earth, called perigee. They can flood low-lying coastal areas on a clear day, and they raise the water level any storm surge is added to.
AQI
The Air Quality Index (AQI) is the U.S. Environmental Protection Agency's color-coded scale for reporting air pollution. It has six categories, from Good (0 to 50) to Hazardous (301 and higher). Values of 101 and above are unhealthy, first for sensitive groups and then, as the number rises, for everyone.
Kp Index
The Kp index is a 0 to 9 scale of global geomagnetic activity, reported in 3-hour intervals from ground-based magnetometers. A Kp of 5 or higher indicates a geomagnetic storm, and the values map onto NOAA's G-scale from G1 (Kp 5) to G5 (Kp 9). The higher the Kp, the farther from the poles the aurora can be seen.
Earthquake Early Warning
A system that detects the fast P-wave near an earthquake's origin and issues an alert before the slower, more damaging shaking arrives, providing seconds to tens of seconds of notice. It is detection, not prediction: the earthquake has already begun. Public systems operate in regions including the U.S. West Coast (ShakeAlert), Japan, and Mexico.
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