Blast of Winter Air Heading for Stateline

December will go down as above average month in terms of temperatures with nearly every day of the month featuring temperatures at or above average. We had one major winter storm, which occurred on the 28th. It dropped significant sleet, ice and snow accumulations across the Stateline and caused numerous problems on the roads.

Now our attention turns towards what's next. For Northern Illinois and Southern Wisconsin, a potent, but relatively dry disturbance in the upper atmosphere will move through the region Wednesday morning into the early afternoon hours from southwest to northeast. It will be accompanied by cold air, so the precipitation it does bring into the region will fall as snow. Snow looks likely, but accumulations look light at this time. By the time the snow showers end--and they should be light to possibly moderate at times--we will see a covering to upwards of an inch or so of accumulation.

As quick as those snow showers move in, they will move out so that by Wednesday afternoon we will be dry, but cloudy. Then, our attention shifts to the very cold air that will push into the region from Canada.

Back on December 23rd, we saw record high temperatures across the area, including a high of 59° in Rockford. Since then, we have seen a steady and steep decline in temperatures. That pattern will continue as we head into the New Year. A downward trend in temperatures is expected to round out 2015 and ring in 2016 as several days in the 20's and teens are forecast, including a high of 18° on New Year's Day. This bitterly cold air will be accompanied by dry conditions, which is good news.

It will be some of the coldest air we have seen thus far this season, especially when you take into account how mild it has been. The reasoning behind why it's going to get cold and potentially stay colder for awhile is because of what we refer as the North Atlantic Oscillation and the Arctic Oscillation. These two teleconnection variables have been positive this winter thus far. However, models are suggesting a more negative trend in both of these as we round out December and enter 2016. When these are negative, that usually means colder air from the Mississippi River to the East Coast.

Here is a visual of what the negative NAO pattern looks like during the winter. Notice the "dip" in the jet stream across the Midwest, Great Lakes, Ohio Valley, Northeast, Mid-Atlantic, and New England. That means colder temperatures and a more active pattern in terms of storm systems. While the majority of storm systems affect the Northeast, Mid-Atlantic and New England, the pattern for the Stateline also becomes slightly more active. Therefore, it looks like colder temperatures are here for awhile, and we could see a few shots of snow as well over the next several weeks.