Indiana’s winter will be just as unpredictable as every other season this year.
A weak El Nino is forming in the Pacific Ocean, which usually produces a warmer than average start to the winter months of December, January, and February. Temperatures are predicted to return to near average by February.
Meanwhile precipitation around the state, according to the Climate Patterns Viewer Decision Support Tool led by Purdue’s Useful 2 Useable initiative, is forecasted to be near average until the end of the winter period, with most climate divisions seeing a slightly drier February.
“With harvest continuing, farmers will have to take advantage of any field time remaining,” said Posey County Purdue Extension Director Hans Schmitz. “As we head into winter, this may include waiting for wet ground to freeze before finishing the harvest.”
The relative strength of the El Nino makes a difference, however, as the El Nino Southern Oscillation is not the only weather oscillation of concern during winter months. The Arctic Oscillation (AO), a wind pattern characteristically located around 55 degrees latitude, can serve to mute or overturn traditional El Nino weather patterns in the winter months.
While the Climate Prediction Center at the National Oceanic and Atmospheric Administration gives a 70 to 75 per cent chance for an El Nino to develop by December, the AO is less predictable and functions on a shorter time scale. Positive values of this index result in confinement of cold air to the poles. Negative values mean cold air can travel slightly further south, at times resulting in the new phrase “polar vortex” and the associated extreme cold weather.
With a weaker El Nino predicted for the upcoming winter months, the activity of the AO may define the kind of winter we receive in Indiana. Current NOAA predictions give no signal for most of the state-neither warmer, colder, wetter, nor drier. The far northern area of the state, Michiana to some, is predicted to be drier and warmer than their average conditions, which lines up well with the El Nino expectations.
Meanwhile, the AO remains positive in value, as it has since April of this year. That six month streak has been replicated 19 times since 1950. Positive AO patterns for eight month streaks or better have only occurred five times over that period, meaning the likelihood of a negative AO value at some point over the winter is high.
Indiana exposed to a negative AO index looks average in precipitation but significantly colder from December-February.