Climate Variability

Climate Versus Weather

Climate is the long-term (monthly or longer) pattern of weather conditions in a region. Climate is not the same as weather.

Weather deals with the short-term movement and development of individual weather systems (fronts, cyclones, air masses).

The earth's climate is a dynamic system, with regional variations on many different time scales from seasonal, to year-to-year, up to decades and even longer.

What are El Niño and La Niña?

El Niño is a warming of the ocean surface along the equator in the Pacific. During a strong El Niño, surface temperatures can rise as much as 15°F above normal from the coast of Peru across the central Pacific. The heat and humidity from El Niño changes global atmospheric circulation and disrupts weather and climate patterns in many regions around the world.

During a La Niña, the same region of the Pacific Ocean cools. Though the temperature change is usually not as drastic, La Niña occurs just as frequently as the better-known El Niño.

El Nino illustration

Neutral is the term used when neither El Niño nor La Niña is present in the Pacific. About half of all years are classified as neutral years.

El Niño and La Niña events tend to repeat roughly every four to seven years, although one is not always followed by the other.

This image shows the unusual warming of the tropical Pacific during the 1997 El Niño (top left) and abnormal cooling during the last La Niña (bottom right),courtesy of NASA.

El Niño Climate Variation Animations

A series of animations are available below from AgroClimate, highlighting the impacts of El Niño and La Niña on precipitation and maximum and minimum temperatures across the United States.

El Nino vs Neutral maximum temperature shift

Example diagram from the movies detailing differences in temperature associated with an El Niño winter.

El Niño/La Niña Impacts Across the Southeast U.S.

The following table provides a summary of the effects on temperature and precipitation across the Southeast:

PhaseRegionOct-DecJan- MarApr-JunJul-Sep
El Nino Peninsular Florida Wet & cool Very Wet & cool Slightly dry Slightly dry to no impact
Tri-State Region Wet Wet Slightly wet No impact
Western Panhandle No impact Wet Slightly Dry No impact
Central and North Ala. & Ga. No impact No impact No impact Slightly Dry
La Niña Peninsular Florida Dry & slightly warm Very dry & warm Slightly wet Slightly cool
Tri-State Region Slighly dry Dry Dry No impact
Western Panhandle Slightly dry Dry Dry No impact
Central and North Ala. & Ga. Dry Dry in the south, wet in NW Ala. No impact Wet in NW Ala.
Neutral All Regions No impact No impact No impact No impact

An important addition not highlighted in the table, however, is the probability of a debilitating freeze across the region during each of these three phases. During a neutral phase, the likelihood of a severe freeze is much greater than during either an El Niño or a La Niña event. Appropriate precautions should be taken to minimize potential losses in the event of a severe freeze during one of these years. For more information on freezes see the AgroClimate Freeze Forecast.