Dave's winter weather forecast

TERRE HAUTE, Ind. (WTHI) - Winter 2009 to 2010, what will happen?

This winter, we are entering a mild El Nino pattern, which will have an impact on our winter weather. First off, we determine the strength of the El Nino by looking at sea surface temperatures in the Pacific Ocean off the western coast of South America. This year, the temperatures are showing that while it's not as strong as past El Nino events, we are finding the waters in this region a little warmer than normal. Consequently, if the waters were to be cooler, we would call that a La Nina pattern.

While this phenomenon of El Nino/La Nina has global effects, we're more interested in the regional effects of the Wabash Valley. This year's mild El Nino pattern looks to bring us a slightly warmer overall winter season. On average, temperatures look to be between one to three degrees warmer for the entire season. While this seems like a relatively small number it can have dramatic impacts on what type of precipitation we receive. Take 29 or 30 degrees, for example. If the temperature on the ground is thirty degrees and we had snow falling it would remain snow and we would see snowflakes reaching the ground. However, if you warm it up three degrees that snow would melt before reaching the ground and would see water reaching the ground. Wait just a few hours later and while the temperatures drop, as they normally do overnight, we would see all water turning to ice. The more liquid precipitation events during the winter months greatly increases our chances to see more icing events. While there are other factors at work, you get the idea.

In summary, If the temperatures look to be slightly warmer we should find the Wabash Valley receiving less snowfall than our average of eighteen inches but more possible rain events. Couple that with some of those temperatures flirting with the 32 degree freezing mark and we could get more ice.