October 4, 2012

By Keith Robinson, Purdue University

After an extremely hot and dry summer, farmers and others might be wondering what kind of weather they can expect for the fall and coming winter.

A variable temperature and precipitation pattern is developing this fall, with September so far a cool and wet month. Indiana average temperatures have run nearly two degrees below normal while precipitation has ranged from near normal in the northern third of the state to more than twice normal in central counties, according to the State Climate Office, based at Purdue University.

Temperatures could remain cool through early October but may turn warm later in the month. The warm weather pattern could continue through November.

The wet trend is forecast to continue through the next two weeks, but conditions drier than normal could prevail for October as a whole. The precipitation outlook for November is less certain, with equal chances of precipitation above normal, normal or below normal at this point.

And what about winter? For now, it’s wait and see. Forecasters are waiting to see how an El Nino develops and how the Arctic Oscillation might influence weather patterns.

“An El Nino generally increases the chances of a warmer and drier Indiana winter, but there is just too much at play at this time, making an outlook challenging,” said State Climatologist Dev Niyogi. Early indications are that an El Niño will develop in early fall.

“However, this El Nino is now expected to be weak and slow to develop such that other factors, such as the Arctic Oscillation and the persistence of the unusual weather patterns we had over the past months, can play a greater role,” he said.

The average weather in individual months can be expected to be more erratic depending on which seasonal element dominates, Niyogi said.

“One month could be warmer than normal and the following colder,” he said. “This high variability will be key as we move into winter this year. So it’s probably going to be more like a little bit of everything this time around.”

Winter weather in Indiana is regulated by elements such as oceanic patterns, including Pacific Ocean surface temperatures and wind circulation around the North Pole. Last year, many forecasters thought Indiana would have a winter similar to that of the previous year: very cold and lots of snow, based in part on how the Arctic Oscillation could have developed. But the weather patterns shifted and moved into a phase that brought warmer air and little snow.

“Recently, we have seen unusual seasonal patterns: the very early start to spring, hot summer and historic drought,” Niyogi said. “What climatology tells us alone will not be the final answer to this winter. My best advice at this stage would be to wait and watch. Sometimes the signals are just not strong enough to make any confident projections – and during a transition such as we are going through with a likely El Nino, change is in the air. We just don’t know which way and how far off from normal the weather will be.”

Niyogi said the State Climate Office will continue to monitor weather patterns and issue another outlook when it has more significant, updated information.