Chris Yates' 2017-2018 Winter Outlook

As temperatures continue to drop in Central Illinois, it's only a matter of time before snow fall across the region. The relatively cold start to November has many wondering what this upcoming winter season will bring to the area. 

There are multiple factors that come in to play when trying to figure out how the upcoming winter season. They are...

  • The El Niño Southern Oscillation (ENSO)
  • Siberian and North American Snow Cover
  • The North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) 
  • Eastern Pacific Oscillation (EPO)
  • Seasonal Climate Models

The El Niño Southern Oscillation

Why you may not realize it, this is the one you are probably most familiar with. While you may not have heard of the El Niño Southern Oscillation, you have heard of it's phases La Niña, Neutral and El Niño. ENSO is a naturally occurring phenomenon that tracks fluctuating sea surface temperatures across the tropical Pacific Ocean. 

El Niño - Warm Phase 

  • This phase occurs when sea surface temperatures are warmer than normal across the eastern tropical Pacific Ocean. This leads to weaker low-level winds along the Equator and enhanced thunderstorm activity across the entire equatorial Pacific Ocean. 
  • The effects of El Niño are often greatest in the winter and tend to bring warmer than normal conditions to northern portions of the United States, including Central Illinois. 

La Niña - Cool Phase This phase occurs when sea surface temperature are cooler than normal across the eastern tropical Pacific Ocean. This leads stronger low-level winds along the Equator and less thunderstorm activity across the entire equatorial Pacific Ocean.

  • La Niña tends to bring cooler than normal and wetter than normal conditions to much of the northern U.S. while warm and dry conditions prevail across the southern U.S.

La Niña conditions are favored for this upcoming winter season. The Climate Prediction Center has stated that there is a 65-75% chance that a weak La Niña will persist through the 2017-2018 winter season. While La Niña winters can be highly variable, Central Illinois has experienced cooler and wetter winters on average. 

Eurasian and North American Snow Cover

This is an area of research that is still relatively new. It is thought that higher than average snow cover across Asia, Europe, and North America in the fall months leads to colder weather across the North American continent during the winter months. Last year, snow cover was below average specifically during the month of November and below average snowfall was experienced during the 2016-2017 winter season, especially across the Midwest. 

This year snow cover is higher, specifically across North America. Theoretically, this should lead to colder Arctic airmass surging southward across the Continental U.S. 

North Atlantic Oscillation and Arctic Oscillation

These two oscillations will influence the number of Arctic airmass that will impact the eastern United States and can fluctuate from every few weeks to multiple months at a time.

North Atlantic Oscillation (NAO)

  • This oscillation is based on sea-level pressure differences between the Subtropical High and the Subpolar Low. The positive phase of the NAO tends to bring warmer than normal temperatures to the eastern U.S. while the negative phase tends to produce colder conditions for the eastern U.S.

Arctic Oscillation (AO)

  • This oscillation is characterized by upper-level winds swirling around the Arctic, a circulation known as the Polar Vortex.
  • When the Arctic Oscillation is in a positive phase it means that the Polar Vortex is stronger, which acts to keep colder temperatures bottled up near the North Pole. When the oscillation is in a negative phase, the Polar Vortex is weaker which allows colder air to spill southward across the United States and tends to lead to cold arctic outbreaks. 

You can think of the Polar Vortex as a top spinning on a table. When the top is spinning fast, the top tends to remain in one spot. Much like the atmosphere, when the winds are swirling quickly around the Arctic the cold air will stay there (strong Polar Vortex).  As the top begins to slow down it will wobble. Similar to the top, a weaker Polar Vortex will cause the jet-stream to wobble allowing for larger dips in the jet stream and colder air to push further south. 

Eastern Pacific Oscillation (EPO)

This oscillation can impact the location of where cold airmass will be across the northern U.S. The EPO is characterized by a variation in the atmospheric flow across the eastern Pacific Ocean.

  • When the EPO is in a positive phase, mild Pacific air flows straight in to the west coast of the United States bringing a significant amount of rain and snow to western parts of the country. However as the flow continues to move east of the Rockies, the air will dry and warm leaving areas east of the Rockies with mild weather, while colder weather tends to be in place across Alaska.
  • When the EPO is in a negative phase, a powerful upper-level ridge develops across the eastern Pacific. This results in warmer temperatures being diverted northward towards Alaska while the cold Alaskan air is then pushed further south in to the northern U.S.

Seasonal Climate Models

In addition to factoring in all of the cycles above, we will also look at multiple climate models. While these models can help point us in a certain direction, they tend to not carry great run to run consistency and quite frankly, are wrong a lot. Still, even looking at incorrect models can prove to be helpful, especially when analyzed correctly and comparing it to recent historical trends.

What Can We Expect This Winter?

I think it's safe to say that this winter will be much different than the past two winter seasons as it appears colder and snowier conditions may evolve over the next three months. There is no one phenomenon that will dictate how this winter plays out, its the complex evolution and interactions between ENSO, the Arctic Oscillation, North Atlantic Oscillation and the Eastern Pacific Oscillation that will define what we will see this winter. 

If we were to spend much of the winter season in the negative phases of these various oscillations, you can bet that it will be a cold winter in Central Illinois. I don't think this will be a record-setting year or a repeat of some of the harsh winters we saw back in 2010-2011 or 2013-2014, but it should be colder and snowier compared to the last few winter seasons.

  • Temperatures - Climate models have shown a great deal of uncertainty when it comes to how temperatures will play out over the next few months. This lowers my confidence in how things will ultimately play out. I think this year will turn in to a more traditional La Niña season and given the recent trend of colder than normal temperatures, I think we'll see this carry over in to December, January, and February. After all, the trend is your friend...until it isn't.  

  • Snowfall - There is a little more confidence in this part of the forecast, though exact snowfall totals is still a shot in the dark. Peoria averages a little more than 24 inches of snow a year. I think we'll see near to above average snowfall through the 2017-2018 winter season. There is no realistic or accurate way to predict exactly how much snow we'll see, but for the sake of putting a number on my prediction of near to above average snowfall I'll take a shot and say we'll see 25 to 35 inches of snow. 


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