Thunderstorms Possible in December?

The calendar may say December, but Mother Nature wants nothing to do with wintry weather across the region. We ended November above average, and we have begun December very mild. In fact, temperatures are going to likely reach record levels on Sunday with lower 60's in the forecast. With the mild weather comes plenty of rainfall for the Stateline tonight into Sunday before ending Monday afternoon.

An area of low pressure is developing in Texas and it will strengthen tonight before lifting northeast towards the Midwest on Sunday. It will draw in plenty of Gulf of Mexico moisture and warmth as it heads in our general direction. Dew points will be in the 50's on Sunday, which is unheard of in the month of December this far north. That is due to the overall strength of the low allowing it draw up rich moisture from the southern states.

The high dew points, warmer temperatures, and high moisture content, in combination with a strengthening low will allow for a lot of rain to fall. In fact, it looks as though the entire Stateline will see 1-2" of rainfall by Monday morning, if not more. The other aspect of this system is the colder air on the back side of the low, which will allow several inches of snow to fall in Kansas with snow showers all the way to the Minnesota-Canada border.

With the high moisture content, warmer temperatures, and strengthening low pressure system also comes the chance of some thunder and lightning tonight. Yes, with Christmas less than two weeks away, we are discussing the chance for thunderstorms in Northern Illinois and Southern Wisconsin. The image to the left shows what the radar will likely look like at 3am tonight. Notice the little areas of orange and red. Those are likely thundershowers and thunderstorms embedded in the rain. Is it a guarantee that we see thunder and lightning tonight? No, but it is definitely in the realm of possibility.

For more reassurance, here is a tool we use sometimes to analyze the potential for thunderstorms. It is the Lightning Threat Index. Whenever values that are above zero show up on this model -- anywhere that isn't white on this map -- the atmosphere is supportive of thunder and lightning within any rain. You can see areas of gray and green on the map, which means thunderstorms are possible for portions of the Stateline tonight into Sunday morning. Thunderstorms are not as likely Sunday afternoon thru Monday morning, but moderate to heavy rain is likely to continue throughout the day on Sunday before ending Monday afternoon.