What will El Nino bring this winter?

• Position: Weather

El Nino has returned, but it is too early to tell how it will impact this winter's weather, according to David Arnold, professor of meteorology, Ball State University, Muncie, Ind. The phenomenon is caused by a shift in wind direction and water temperature in the equatorial Pacific Ocean. El Nino can bring about a change in typical weather conditions, sometimes with disastrous results.

Arnold stresses that "It is important to realize that interpreting the impact of any El Nino event is not always a straightforward matter since each one is somewhat unique. Considerable variability exists between El Nino years. Subtle differences between some El Nino winters may produce unexpected results A seemingly minor change in the character of the mid-level water circulation pattern can bring about much-different conditions at the surface than ware anticipated. For example, the El Nino event of 1976-1977 marked the first in a series of three of the coldest consecutive winter seasons in the Midwest," he indicates.

An El Nino condition exists when an unusual warm pool of sea-surface temperatures exists over the Pacific in the vicinity of the International Dateline. This ocean-surface temperature...