January 26, 2000

La Niña Brings Changes in the Weather

Can a slight change in the surface temperature of the Pacific Ocean 8,000 miles away affect the weather in your part of the world for the entire winter? Absolutely, say meteorologists who study the periodic weather pattern know as La Niña. During the winter months, in fact, North America faces some of La Niña's greatest impacts on temperature, wind, rain, and snow.

The present La Niña is in its second year and could last until Spring, making it one of the strongest La Niñas in decades. How many of this season's La Niña predictions have come true where you live and in other parts of the country?

During La Niña periods, the surface temperature recorded by buoys in the eastern Pacific Ocean decreases. This year's readings have averaged more than 1 °C below normal. That may not seem like much, but as the map below indicates, La Niña brings changes to the weather around the world.

La Niña map

Focus on the U.S.
This time of year, though, the United States bears many of those changes. Using the chart below, decide whether some of the predictions related to La Niña have actually come to pass this year. For each of your answers, provide some specific examples from the weather information you find at the following sites:

  • Monthly Temperature Summaries In this National Weather Service table, you can find temperatures for cities around the country as well as their average departure from normal (see the 9th column, marked AVE DEP NORMAL).
  • Drought Impacts provides a color-coded map that shows which areas of the U.S. are unusually dry.
  • Compare the National Hurricane Center's maps of the 1999 Atlantic hurricane season and the 1997 season--the last one before the current La Niña cycle began.

Prediction table

The effects of La Niña represent only half of an even more complicated weather story. What's the other half?

Brother, Sister Act

La Niña is the sister of a more famous brother--El Niño, the unusual warming of the waters in the eastern Pacific Ocean, which last made its appearance in 1997. These two weather patterns--which often have opposite effects on the countries they visit--form a complete cycle on an average of 3-5 years. Over the past half century, El Niños have been present 31% of the time and La Niñas 23% of the time.

Temperature comparison

NOAA's satellite images of the Pacific Ocean near the Equator show the contrast between surface temperatures during the recent La Niña phase and the El Niño that preceded it.

Notice in the right image how the cooler (blue color) temperatures extend from South America into the eastern part of the Pacific Ocean, whereas on the left, the warmer (red color) temperatures dominate almost the entire stretch from Asia to the Americas.

Niña vs. Niño

Related Activities and Information
There are plenty of good resources available to enlarge your understanding of this powerful cycle and other weather-related phenomena.

  • The National Oceanographic and Atmospheric Administration (NOAA) maintains an extensive La Niña Web site, including an in-depth listing of Frequently Asked Questions.
  • The GLOBE Network--Global Learning and Observations to Benefit the Environment--is operated by NOAA. Seven thousand schools worldwide connect to research scientists and share student-generated data on the environment.
  • El Niño, La Niña, and the Southern Oscillation (International Geophysics Series, vol. 46), by S. George Philander, studies the dynamics of the El Niño-La Niña cycle.
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