A Minute With...

Eric Snodgrass, expert on atmospheric sciences

2/14/2012  8:00 am

Throughout most of the U.S., this winter has been one of the warmest in memory. There has been less snow, too. Are we experiencing global warming or just a periodically warm winter? And what, if anything, does this winter portend for spring and summer? Eric Snodgrass, an atmospheric sciences instructor, was interviewed by Cailun Gangi, a student intern in the U. of I. News Bureau.

We’ve seen unusual weather before but this seems to be more drastic than previous seasons. What are the underlying contributors to such above-average temperatures?

image of eric snodgrassThis winter season has seen an interesting combination of weather events that have made forecasting quite challenging. 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 Nina conditions across the equatorial Pacific Ocean. A La Nina 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 Nina should produce colder and snowier conditions across portions of the Midwest. Last year, the La Nina helped push Chicago well over its snowfall average and Champaign had more than 41 inches of snow (26 inches is average).

Although the La Nina has persisted into this winter, a distinct difference for our area has been the lack of cold air. We have been getting the precipitation, but because it has been on average 10-15 degrees F warmer than normal, much of this has fallen as rain. We are currently at 8.6 inches of snow while last year at this time we were on our way to 40 inches. Why the difference? Where has the cold air been? The answer is the phase of the Arctic Oscillation and Europe, respectively. The Arctic Oscillation (AO) is a weather pattern meteorologists watch closely to forecast the presence and location of cold air in the Arctic. 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 (November through late January), the AO has been in its positive phase. So despite La Nina’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 this week (of Feb. 5).

Can we expect the upcoming seasons to hold such unusual weather as well?

That is very difficult to project. Currently, the La Nina 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. 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.

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.

Is climate changing due to anthropogenic causes? Yes, absolutely. Is this an example of climate change? No, this is simply a series of weather events.

Since there has been so much rain and fog recently, can we expect to have a dry spring?

Great question! There is no possible way to use the rain and fog that we have seen recently to predict the weather of the coming spring. For some reason, people tend to think that one extreme leads to another when it comes to weather and I am not sure where that thinking has come from. Looking at the long-term forecasts from the Climate Prediction Center, March through May is forecast to have slightly above normal temperatures and normal precipitation amounts. It is important to know that giving a three-month forecast like this has little skill and accuracy. We are attempting to predict the highly variable nature of a chaotic system – the atmosphere – and forecasts like this need to be taken with a large grain of salt.

With extreme weather proliferating across the nation, do you foresee Illinois getting hit with something harder than just rising temperatures?

Extreme weather is nothing new; we are just hearing more and more about it in the news media. For example, Texas is in the middle of its worst one-year drought in history. However, this drought doesn’t even compare to the drought Texas experienced during the 1950s or 1930s. I am not trying to downplay this drought – it is serious – but it’s not the first time something like this has happened. In Illinois, it is warm and there has not been much snow, but we are a long way away from setting records for either warm temperatures or low snowfall. Even with the tornadoes in the U.S. last year, which were the deadliest we have seen in a long time, the number of tornadoes was not record setting and in our country’s past there have been much deadlier events.

So, to say that I foresee Illinois getting hit with something harder than a warm winter is nearly impossible to project. Forecasting long-term weather events (not climate events) is simply something our science has not been able to do accurately.

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