As recently as six weeks ago, most weather forecasters were talking about an El Nino winter. Now, the most recent information from the National Weather Service indicates they are discounting the impact of El Nino. In fact, they are not even considering El Nino as a factor in the winter forecast for most areas of the U.S. at the present time.
"The El Nino is just so weak that it may not be a factor," says Ken Scheeringa, associate Indiana state climatologist. "We're in a cycle that favors La Ninas over El Ninos, and although an El Nino tried to form, it's just not developing as expected."
El Nino and La Nina refer to warming and cooling of Pacific Ocean waters, usually in the tropical Pacific. The change in temperature at sea level is important because it affects barometric pressure, which in turn affects circulation patterns aloft. These circulation patterns affect movement of weather systems around the globe.
So instead, Scheeringa is looking for an up and down winter in the Eastern Corn Belt, and in Indiana, in particular. This means he expects period of warm to very warm weather and periods of cold to very cold weather embedded within the upcoming winter. The National Weather Service says this winter has an equal chance of above normal, normal, or below normal temperature and precipitation, but the climatologist says that hardly tells the story.
In the end it may look average by the numbers, but there may be extreme warm and extreme cool periods in between. Snow should be part of that mix, he says.
Other factors besides El Nino and La Nina can affect Indiana weather. One factor is the Arctic Oscillation pattern. It has played a role in the past two winters. The problem, he says, is that it develops quickly, and it's difficult to understand what impact it might have more than two weeks in advance. That's not helpful to a long-range forecaster trying to predict winter weather.