Scientists at the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center reported today that El Niño conditions have developed in the tropical Pacific and are likely to continue into early 2007. Ocean temperatures increased remarkably in the equatorial Pacific during the last two weeks. "Currently, weak El Niño conditions exist, but there is a potential for this event to strengthen into a moderate event by winter," said Vernon Kousky, NOAA's lead El Niño forecaster.

Typical El Niño effects are likely to develop over North America during the upcoming ski and snowboard season. Those include warmer-than-average temperatures over western and central Canada, and over the western and northern United States. Drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest, while above-average snowfall is forecast for parts of the Southwestern U.S.

Near the end of each calendar year ocean surface temperatures warm along the coasts of Ecuador and northern Peru. Local residents referred to this seasonal warming as "El Niño", meaning The Child, due to its appearance around the Christmas season. Every two to seven years a much stronger warming appears, which is often accompanied by beneficial rainfall in the arid coastal regions of these two countries. Over time the term "El Niño" began to be used in reference to these major warm episodes.

El Niño is closely related to a global atmospheric oscillation known as the Southern Oscillation (SO). During El Niño episodes lower than normal pressure is observed over the eastern tropical Pacific and higher than normal pressure is found over Indonesia and northern Australia. This pattern of pressure is associated with weaker than normal near-surface equatorial easterly (east-to-west) winds, often referred to as the trade winds. These features characterize the warm phase of the SO, which is often referred to as an El Niño/Southern Oscillation (ENSO) episode.

The increased heating of the tropical atmosphere over the central and eastern Pacific during warm episodes, affects atmospheric circulation features, such as the jet streams in the subtropics and in the temperate latitudes of the winter hemisphere. The jet streams over the eastern Pacific Ocean are stronger than normal during warm episodes (see seasonal atmospheric circulation features). Also, during warm episodes extratropical storms and frontal systems follow paths that are significantly different from normal, resulting in persistent temperature and precipitation anomalies in many regions.

Some impacts from the developing El Niño are already evident in the pattern of tropical precipitation. During the last 30 days, drier-than-average conditions have been observed across all of Indonesia, Malaysia and most of the Philippines, which are usually the first areas to experience ENSO-related impacts. This dryness can be expected to continue, on average, for the remainder of 2006.

Also, the development of weak El Niño conditions helps explain why this Atlantic hurricane season has been less active than was previously expected. El Niño typically acts to suppress hurricane activity by increasing the vertical wind shear over the Caribbean Sea region. However, at this time the El Niño impacts on Atlantic hurricanes are small. "We are still in the peak months of the Atlantic hurricane season, and conditions remain generally conducive for hurricane formation," said Gerry Bell, NOAA's lead seasonal hurricane forecaster.

But what does this mean to skiers and snowboarders? During a warm episode winter, mid-latitude low pressure systems tend to be more vigorous than normal in the region of the eastern North Pacific. These systems pump abnormally warm air into western Canada, Alaska and the extreme northern portion of the contiguous United States. As the images to the right indicate, El Nino years often translate into below-normal snowfall across broad regions spanning the U.S.-Canada border, including the northern Rockies, the Ohio Valley, and the Adirondack Mountains of upstate New York. Higher than normal snowfall typically falls across the ski and snowboard resorts of the southwestern U.S. in northern New Mexico, northern Arizona, southwestern Colorado and southern Utah.