Dear Tom,
What do you think the coming winter will be like?
—Steve Craig, Berwyn
Dear Steve,
It's likely to be more turbulent than usual. The odds (56-60 percent) favor above-normal precipitation, more snowfall than normal and especially volatile temperatures.
Here's the rationale. Surface water temperatures in the tropical Pacific Ocean have global impact on the Earth's weather and climate, and they are often potent indicators of winter weather in the Northern Hemisphere. "La Nina" involves cooling of the water in the equatorial Pacific westward from South America; its counterpart, "El Nino," involves warming.
The National Weather Service's Climate Prediction Center indicates a La Nina event, beginning now, will persist through the winter. Our estimate of an active winter is based upon an in-house analysis of nine previous La Nina winters in Chicago.
