ROCKFORD, Ill. (WTVO) — The winter chill has set in, and it looks like it may be staying for at least a little while.

We’re expecting La Niña conditions once again for the upcoming winter season.  This could bring quite a bit of variability in both temperatures and precipitation for us here in northern Illinois. According to the National Weather Service in Chicago, this will be our third winter in a La Niña oscillation.

Since the 1950s, there have only been two other times where three consecutive La Niña events occurred: 1973-1976 and 1998-2001.  

La Niña oscillations normally happen when trade winds push warmer surface water towards Asia. In certain years, trade winds are stronger, which causes cooler water to surface in the Eastern Pacific. This drives cooler air into the Pacific Northwest and northern Great Plains.  For the Tennessee and Ohio Valleys, as well as the Pacific Northwest, a wetter pattern can be expected. For areas in Florida and the deep south, a drier and warmer winter pattern.

During an El Niño oscillation, trade winds weaken which pushes warmer water off the coasts of South America. This drives a warmer pattern for areas in the northwestern Midwest and Pacific Northwest along with the northern Great Plains. For the deep south, the coastal southeastern U.S. and southern California, a wetter pattern. For the Tennessee and Ohio Valleys, typically a drier pattern.

National Weather Service Meteorologist, Ricky Castro, says La Niña and El Niño play a role in the mean jet stream pattern and storm track during the winter season, “On average, a La Niña, and there’s certainly exceptions, can lead to an active storm track kind of near or just north of the Ohio Valley during a decent chunk of the winter.”

Castro says there is a good chance of seeing above-normal precipitation near our area this season.

Castro says it’s common to have large temperature swings due to an active storm track, “As a really good example of that, one of the most active recent La Niña’s was 2007-2008 was actually the second snowiest on record for Rockford, so obviously a really active pattern, but that winter had a really substantial warm up in early January, there was even a tornado that started in Boone County and went into McHenry County in early January. It basically melted the snowpack from December, and it was in the 60s on January 78th and there were tornadoes that day. So that’s kind of like a classic, really active, really back and forth La Niña pattern.”

This does not mean we will see significant tornadoes, but it is not all that uncommon to have a setup for thunderstorms or severe weather when you have bigger warmups.

During a La Niña pattern, volatility is common, “We could have lots of swings along the way, and it could still end up near average. Making up that we’ll have plenty of cold and plenty of warm.”

We’ve already had our first trace of snow for the season, back on October 17th.  This was a little earlier than normal, with the first trace of snow usually taking place closer to Halloween. We don’t usually have our first one-inch snow event until December 5th which came earlier this year, on November 15th.