How To Understand A Weather Forecast

National Weather Service forecast for winter is a prime example.

Published on: Nov 9, 2012

At first glance it appears that the National Weather Service is forecasting a normal winter for Indiana and the Eastern Corn Belt. That's what Ken Scheeringa, associate state climatologist in Indiana, said. At least that's what I thought he said.

What he really said, and what the National Weather Service forecast actually says, is something different. At the current time the NWS forecast is for 'equal chances of above normal, normal and below normal' temperature and precipitation this winter.

"That's very different than normal," Scheeringa says. "They are not predicting a normal winter. Instead, they're saying the winter could go any direction. Anything is possible.  When they say equal chances, they mean the winter could be above normal for that factor, or below normal, or it could wind up normal."

National Weather Service forecast for winter is hard to understand
National Weather Service forecast for winter is hard to understand

Scheeringa says at this time, NWS doesn't have solid information to know which way Indiana's winter weather will go.

By saying it could go any direction, Scheeringa, who agrees with the forecast, believes it means this could be an up and down winter, with periods of both warm spells and cold spells interspersed during the winter. Snow would likely be part of the mix during the cold periods.

One reason why NWS isn't able to make a definitive long-term forecast for winter is because of the absence of strong factors that normally control weather over the U.S.

The strongest is the El Nino/La Nina cycle, and the El Nino which was trying to develop has stalled out. It would be a period of warmer than normal temperatures in the Pacific Ocean. Because it's stalled out, the NWS at this point doesn't believe it will impact winter here. El Nino winters have certain characteristics. Without that factor in play, other factors will influence weather, but most of them change more quickly and are harder to predict that the El Nino or La Nina.