While it certainly hasn’t been feeling like it, winter weather is not too far away. The leaves are changing colors and temperatures are slowly getting colder. There has been a lot of speculation as to what this winter season will bring over the past few weeks and no one will know for certain how things will pan out. With that said, here is what I think will happen in Central Illinois during the 2016-2017 winter season.
When trying to predict what will happen over the course of a season it’s important to look at factors not just locally but globally.
Many of you are familiar with the terms El Niño and La Niña. You may not remember what each one means exactly but you probably know that whatever it is can impact our weather here in Central Illinois. Here’s a brief (and overly simplified) break down of each.
An El Niño climate pattern occurs when temperatures in the eastern Pacific are above average. These warmer sea surface temperatures help generate more clouds and storms across the southern U.S. resulting in cooler weather in the southern half of the country while warmer and drier weather typically occurs across the northern half.
A La Niña climate pattern occurs when temperatures in the eastern Pacific are below average. Cooler sea surface temperatures will limit the amount of clouds and storms that develop across the southern U.S. typically resulting in warmer and drier weather across the south. (See Figure 1a & b) Northern portions of the U.S. will typically see cooler and wetter conditions but, the weather during La Niña climate patterns can often be very volatile making long range prediction difficult.
The changing pattern between La Niña and El Nño is called the El Niño Southern Oscillation.
If you think back to last winter you may remember we were in an El Niño climate pattern, but not just any El Niño. It was one of the strongest El Niños on record! (See Figure 2) Thanks to this very strong El Niño, Central Illinois experienced temperatures that were well above average, below average snowfall and above average rainfall.
In the past, once we’ve gone through a strong to very strong El Niño we have typically fallen in to a moderate to strong La Niña, but not this year. This year we have fallen in to weak La Niña which could help keep this upcoming winter a little closer to a “typical” Central Illinois winter.
There are other patterns to keep an eye on over the course of the next few months that will also impact how this upcoming winter shapes up.
There is another pattern known as the Arctic Oscillation that changes over the course of 2-4 weeks. This pattern change depends on the location of high pressure over the Arctic and Siberian snow cover.
The Arctic Oscillation (AO) is characterized by winds moving counter clockwise across the northern hemisphere. This large scale counterclockwise circulation is know as the Polar Vortex, another term many of you are familiar with, though you’ve probably heard it used incorrectly.
When the AO is in a positive phase, it means the Polar Vortex is stronger and that winds rotating around the North Pole are stronger keeping the cold, arctic air up near the North Pole. (See Figure 3) When the AO shifts in to a negative phase, the Polar Vortex and winds rotating around the North Pole have become weaker allowing colder temperatures to escape the higher latitudes and move down in to the Central U.S. (See Figure 4)
You can kind of visualize the Polar Vortex as a top spinning on a table. When the top is spinning fast, the top tends to rotate very tightly. This is similar to a strong Polar Vortex. As the rotation begins to slow down the top will begin to wobble. This is similar to a weak Polar Vortex where the wobbling motion of the top simulates the colder temperatures wobbling away from the North Pole!
So why is the Arctic Oscillation important?
Since we will already be in a weak La Niña much of the northern U.S. will be susceptible to cold air outbreaks. This in conjunction with negative phases of the Arctic Oscillation could mean higher chances of seeing arctic outbreaks across the the U.S.
During El Niño years, the affects of a negative phased Arctic Oscillation could be offset by the warm temperatures moving in off of the eastern Pacific…which occurred last winter.
So here is my BOLD 2016-2017 Winter Outlook…
- We are still feeling the effects of last year’s very strong El Niño, so it could very well be a late start to Winter in Central Illinois. Peoria’s average 1st measurable snowfall is November 23rd, so don’t be surprised if we don’t see our first snow until late November or early December.
- I project that between the months of December, January and February (Meteorological Winter) Peoria will receive 19-24 inches of snow. (Peoria averages 19.5″ of snow over the course of those 3 months)
- Between December, January and February I project that Peoria will see near average temperatures with an average daily temperature between 27°-28°. It will likely be a mild start to this winter season but colder air and arctic outbreaks could impact the area in early 2017.
- I am also projecting that Peoria will end up with near to above average rain (liquid precipitation or melted snow) with 6.0″ to 8.0″ of rain between December, January and February.
- Finally, we could very well end up with a late Spring in Central Illinois. The average last snow in Peoria occurs on March 18th. Depending on how long the effects of this weak La Niña hangs around, Central Illinois could see additional snow in late March and/or very early April, allowing Peoria to close in on 30 inches of snow for the season which is above the yearly average of 24 inches.
While we will almost certainly see a few bad winter storms rolling through the region this year, it should not be a blockbuster winter season. However, you should expect this winter season to be snowier and colder than that of last winter. You should also expect a lot of volatility (very warm to very cold) in the weather throughout this winter season.