With one month to go before the official start of spring, the winter of 2011-12 is proving to be one of the warmest on record.
It's certainly a far cry from the blustery, frigid winter of 2010-11, a season that dumped copious amounts of snow and freezing rain on Crawford and its neighboring counties, causing thousands of dollars in damage, dozens of cancellations and week-long power outages.
Since Dec. 1, the average daytime high in Crawford County has been 44.35 degrees, up from 33.5 degrees for the same period a year earlier. Highs in the 50s have been common, even in early February and the mercury hit the low 60s in both December and January.
The average overnight low here this winter so far has been 28.65, up from 20.6 a year before. While January has a fair share of nights in the teens, the temperature often failed to dip below 40 on many nights during the past two and a half months.
Last winter was considerably snowier. A long stretch of cold temperatures combined with snow and an ice storm during the first few days of February last year. More than 19.01 inches of white stuff had been reported here by mid-February 2011. This winter, there has been only 4.75 inches of snow - and none of it lasted very long.
The county has seen more rain this winter. Crawford County received 4.02 inches of rain and 1.49 inches of freezing rain last winter. This year, 10.45 inches of rain has been reported. Small amounts of freezing rain were mixed in with regular rain Jan. 21 and 22.
Eric Snodgrass, an atmospheric sciences instructor at the University of Illinois, said this winter has surprised weather prognosticators.
"This winter season has seen an interesting combination of weather events that have made forecasting quite challenging," Snodgrass said. "The main story going into the winter was one of cold weather and lots of snow - just like last winter. This forecast was based on continuing La Niña conditions across the equatorial Pacific Ocean."
He explained a La Niña occurs when the sea surface temperatures are colder than average across the Pacific Ocean between the west coast of South America near Peru and Australia.
"Holding all other things constant, a La Niña should produce colder and snowier conditions across portions of the Midwest. Last year, the La Niña helped push Chicago well over its snowfall average and Champaign had more than 41 inches of snow - 26 inches is average," he said.
Although the La Niña has persisted into this winter, a distinct difference for Illinois has been the lack of cold air. "We have been getting the precipitation, but because it has been on average 10 to 15 degrees warmer than normal, much of this has fallen as rain," Snodgrass said. He credits a different weather phenomena, the Arctic Oscillation, for the warmer air.
"The Arctic Oscillation is a weather pattern meteorologists watch closely to forecast the presence and location of cold air in the Arctic," he explained. "We have developed an index to help us predict the movement, pressure and temperature of this air and the easiest way to use this index is to watch for it to shift between its positive and negative values. When the AO is positive, lower air pressure tends to dominate the Arctic weather and traps the cold air far north preventing it from intruding south where we live. When negative, higher air pressure forms and the cold air frequently slides southward over the Midwest.
"For much of this winter, the AO has been in its positive phase. So despite La Niña's best efforts to bring more snow to our area, the lack of cold air has turned this snow to rain. It has not been until just recently that the AO has turned negative and as a result we have had snow twice recently," he added.
La Niña is weakening and spring is approaching. "Long-term weather forecasting - beyond 10 days - has very little skill and accuracy, and it is folly to put a lot of stake in long-term weather forecasts," Snodgrass said. "It is important to note here that weather forecasting and climate projections are two entirely different methods of modeling the behavior of the atmosphere.
"Many will try to blame this winter weather on climate change or global warming, and it is crucial to understand that weather and climate are not the same," he said. "Climate is the average of weather. For example, last winter we had 41 inches of snow in Champaign; this winter we might struggle to get to 14 inches. Average these years and it matches the climatological average for Champaign - a record that goes back to the late 1800s."