December Outlook

The month of December was expected to be warmer than average when the outlooks were released months ago. The pattern has continued to appear that way as we approach the first day of December. Warmer than average temperatures appear likely across the northern half of the country with the higher probabilities of seeing those warmer than average temperatures existing across the Northern Plains, Upper Midwest and Great Lakes, including Southern Wisconsin and Northern Illinois.

The reasoning behind the warmer than normal temperatures for the Pacific Northwest and North-Central United States is because a strong El Niño taking shape this winter, in addition to blocking of the upper level pattern (high pressure) that is located over the North-Central Atlantic Ocean.

Another aspect of El Niño for the Illinois and Wisconsin region is less-than-typical precipitation. As the full effects of the El Niño pattern settle in during December, we will begin to see a shift in the pattern to drier than normal for the Northern Plains and Upper Midwest. That will begin in December, and the entire winter period is expected to be drier than normal for the Stateline.

However, it is with less confidence that we will see drier than normal weather in December than it is that we will see warmer than normal temperatures. This is because temperature trends are showing up with greater evidence of seeing above average warmth. In addition, the drier portion of El Niño may not arrive until January across the region. The outlook for then may feature higher probabilities of seeing below normal precipitation.