You may remember back in late November and early December, some forecasters called for a winter similar to 2010-2011, with cold outbreaks and the chance for significant amounts of snow. Instead what Indiana saw in most regions was the fifth-warmest winter since 1930 and snow totals that were significantly below normal in most areas.
Winter ends now on the calendar by the seasons. For climatologists that deal with data, the winter period is Dec .1 to March 1, so it ended three weeks ago. The fifth-warmest winter since 1930 is based upon the Dec. 1 through February 29 reporting period.
The Indiana state climate office was one of the groups that expected a winter in Indiana similar to last year. Ken Scheeringa, assistant state climatologist, explains why their prediction didn't prove to be accurate.
"We were basing a good part of our projections on long-term weather maps and what it appeared La Nina would due," he says. La Nina was strengthening again at the time. It appeared that would set things up for a winter with cold temperatures and snowfall, much like the previous winter.
There are other factors, sometimes called forcing functions, that impact weather, Scheeringa explains. The El Nino/La Nina cycle gets the most publicity because it is typically one of the strongest players. It is based on ocean temperatures in the western pacific, that affect barometric pressures, which in turn affect circulation patterns aloft. That in turn affects the Jet Stream, which plays a huge role in blocking or allowing storm fronts and cold vs. warm air to enter a region.
However, it's not the only factor. Another one that can impact winter weather is Indiana is the Arctic Oscillation. "We noted last fall that it would play a role," Scheeringa recalls. However, they weren't sure what role it would play. At the time, they figured it would behave much as it did during the previous winter,. If that happened then the La Nina, strengthening itself again, would result in a colder than normal winter with snow.
Instead the Artic Oscillation turned out to do the exact opposite as compared to the previous winter, Scheeringa notes. That impacted the Jet Stream, overriding any influence from the building La Nina. The repositioning of the Jet Stream compared to what was expected blocked cold air outbreak sand prevented them from flowing into the center of the country, including Indiana.