El Niño and La Niña occur on average every 3 to 5 years. However, in the historical record the interval between events has varied from 2 to 7 years. According to the National Centers for Environmental Prediction, this century's previous La Niñas began in 1903, 1906, 1909, 1916, 1924, 1928, 1938, 1950, 1954, 1964, 1970, 1973, 1975, 1988, and 1995. These events typically continued into the following spring.

La Niña conditions typically last approximately 9-12 months. Some episodes may persist for as long as two years.

El Niño and La Niña are extreme phases of a naturally occurring climate cycle referred to as El Niño/Southern Oscillation. Both terms refer to large-scale changes in sea-surface temperature across the eastern tropical Pacific. Usually, sea-surface readings off South America's west coast range from the 60s to 70s F, while they exceed 80 degrees F in the "warm pool" located in the central and western Pacific.

El Niño and La Niña result from interaction between the surface of the ocean and the atmosphere in the tropical Pacific. Changes in the ocean impact the atmosphere and climate patterns around the globe. In turn, changes in the atmosphere impact the ocean temperatures and currents. The system oscillates between warm (El Niño) to neutral (or cold La Niña) conditions with an on average every 3-4 years.

Both El Niño and La Niña impact global and U.S. climate patterns. In many locations, especially in the tropics, La Niña (or cold episodes) produces the opposite climate variations from El Niño. For instance, parts of Australia and Indonesia are prone to drought during El Niño, but are typically wetter than normal during La Niña.

La Niña often features drier than normal conditions in the Southwest in late summer through the subsequent winter. Drier than normal conditions also typically occur in the Central Plains in the fall and in the Southeast in the winter. In contrast, the Pacific Northwest is more likely to be wetter than normal in the late fall and early winter with the presence of a well-established La Niña.

The jury is still out on this. Are we likely to see more El Niños because of global warming? Will they be more intense? These are the main research questions facing the science community today. Research will help us separate the natural climate variability from any trends due to man's activities. We cannot figure out the "fingerprint" of global warming if we cannot sort out what the natural variability does.

Absolutely, and rather drastically in the case of the stronger events, such as 1997/98. If all that occurred during an El Niño were a warming of the equatorial ocean where nobody lives, El Niño would not occupy the public awareness as it now does.

They do indeed vary to some extent. Here's the accurate, if somewhat technical explanation from NOAA/Climate Prediction Center: quot;In response to the more uniform pattern of heating in the tropics during an El Niño the wintertime jet streams in each hemisphere tend to be more uniform from east to west and extend farther east than normal.

Scientists from NOAA and other agencies use a variety of tools and techniques to monitor and forecast changes in the Pacific Ocean and the impact of those changes on global weather patterns. In the tropical Pacific Ocean, El Niño is detected by many methods, including satellites, moored buoys, drifting buoys, sea level analysis, and expendable buoys.

Since a strong jet stream is an important ingredient for severe weather, the position of the jet stream determines the regions more likely to experience tornadoes. Contrasting El Niño and La Niña winters, the jet stream over the United States is considerably different. During El Niño the jet stream is oriented from west to east over the northern Gulf of Mexico and northern Florida. Thus this region is most susceptible to severe weather.

Dr. William Gray at the Colorado State University has pioneered research efforts leading to the discovery of La Niña impacts on Atlantic hurricane activity, and to the first and, presently only, operational long-range forecasts of Atlantic basin hurricane activity. According to this research, the chances for the continental U.S. and the Caribbean Islands to experience hurricane activity increases substantially during La Niña.

It is inaccurate to label individual storms or events as a La Niña or El Niño event. Rather, these climate extremes affect the position and intensity of the jet streams, which in turn affect the intensity and track of storms. During La Niña, the normal climate patterns are enhanced. For example, in areas that would normally experience a wet winter, conditions would likely be wetter than normal.

NOAA's Climate Prediction Center issues monthly long lead climate outlooks that extend for the next 13 months. The forecast issued on July 16, 1998, calls for continued above normal temperatures throughout most of the Southwest U.S. and southern Florida in the late summer and fall. Into the fall, warmer than normal temperatures are forecast for much of the Southwest including Texas, New Mexico, Arizona, and portions of Colorado.

Weather will impact the world to a degree, for instance, in a place where it snows snow will be seen on the ground.

During drought conditions and in the winter, roots will travel long distances in search of moisture. When trees and shrubs get thirsty, they follow the trail of moisture vapors escaping from small cracks, holes, or poorly sealed joints in the water and sewer lines. The roots penetrate the opening to reach the nutrients and moisture inside the pipes.

Bioheat® fuel has similar cold weather properties as the heating oil it is made from. Bioheat® fuel Blends up to 20% biodiesel may increase the cold flow properties approximately 2-5 degrees Fahrenheit from the base heating oil it is blended with. If cold weather handling and usage are a concern with regular home heating oil, they will be a concern with Bioheat® fuel.

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There have only been two strong La Niña events. Although scientists have looked for a correlation between La Niña and tornadoes, there just isn't enough data to make any conclusions.