Peoria, Ill. (WMBD) – It’s that time of year to lay out my bold prediction for the next 3 months and tell you what I see playing out in Central Illinois this winter. In this article we’ll take a look at where we stand with the El Niño Southern Oscillation (ENSO) and what that could mean in the coming months. We’ll also take a look back at what has happened under similar conditions in the past and how short term patterns called teleconnections will help shape the weather over the next few months.
- Weak to moderate La Niña conditions expected through the winter with a 50-50 chance it persist through Spring
- Near to below average temperatures expected
- Above average precipitation expected
- Near average snowfall expected
Average Winter Conditions for Peoria
- Average Daily Temperature – 28.8°
- Average Precipitation – 6.26″
- Average Snowfall – 26.2″
For the second straight winter, La Niña conditions are present across the Equatorial Pacific and they are expected to remain in place through the upcoming winter season. While it won’t be the only factor in determining what will happen this winter, this “double-dip La Niña” could still have an influence on our upcoming winter.
What is the El Niño Southern Oscillation (ENSO)?
It’s often highlighted in seasonal forecasts such as this to help determine how the weather across the U.S. will be impacted. There are three phases to ENSO that are determined by monitoring sea surface temperatures and wind patterns over the Pacific Ocean.
- El Niño (Positive Phase) – This phase occurs when sea surface temperatures across the central and eastern Pacific are above average. This often results in less rainfall over Indonesia and increased rainfall across the central and eastern Pacific. Shifting winds near the equator will carry tropical moisture north into North America. This typically leads to cooler and wetter seasons across the southern U.S. while warmer and drier seasons occur across the northern U.S.
- La Niña (Negative Phase) – In this phase, sea surface temperatures across the central and eastern Pacific are below average and rainfall often increases across Indonesia. The sub-tropical jet stream weakens and polar jet becomes the main driving force for storms across the U.S. and results in dry and warm conditions across the southern U.S. while the northern part of the country sees cooler and wetter seasons.
- Neutral Phase – Sea surface temperatures across the central and eastern Pacific Ocean are near average and there for “neutral”. While the direct impacts of this phase are often minimal, warm and wet conditions typically prevail in the southeast U.S. while colder conditions linger across the northern U.S.
Since this upcoming winter is a double dip La Niña its worth looking at what has played out during past double-dip La Niñas.
The pattern shows that double-dip La Niñas have historically produced cooler than average temperatures across the west, northwest and northern plains while warmer temperatures were seen across the south. When it comes to precipitation, wetter conditions were seen across the northern Rockies and parts of the Midwest while the southwest, southeast and east coast experienced below average precipitation.
Despite all of these trends and averages, its important to remember that La Niña winters are highly variable across the Midwest and no two La Niñas are identical. No matter the phase of ENSO, each El Niño and La Niña are different and usually don’t look exactly like the “typical pattern” seen in text books. That’s because smaller scale patterns known as teleconnections will ultimately determine how the winter season will play out. Unfortunately the predictability of these patterns only extends out a few weeks so understanding what they are going to do months in advance is not possible.
Teleconnections and How They Impact Us
The following teleconnections will help shape our upcoming winter season. Here is what they are and how they influence our weather…
The Arctic Oscillation (AO)
The Arctic Oscillation is a short term teleconnection that determines how much cold air will impact the eastern U.S. Unlike ENSO, the predictability of the Arctic Oscillation only extends a few weeks out. The phase of the AO is characterized by the strength of the winds circulating counterclockwise around the north pole, a phenomenon known as the Polar Vortex.
- Positive Phase – This phase of the AO indicates that the Polar Vortex is strong. This produces stronger westerly flow around the Arctic which confines colder air to the Arctic Circle.
- Negative Phase – The Polar Vortex is in a weakened state and the jet stream becomes highly amplified and sends arctic air south. In Central Illinois, a negative phase of the AO often results in more frequent arctic air masses and increased storminess making for some rather uncomfortable stretches of winter weather.
North Atlantic Oscillation (NAO)
The North Atlantic Oscillation is based on sea-level pressure difference between the Azores High and the Subpolar Low. Similar to the AO, the NAO is only predictable a few weeks out.
- Positive Phase – This phase of the NAO means that there is a significant difference in pressure between the Azores High and the Subpolar Low, in other words, both the high and the low are strong. This makes the jet stream winds over the north Atlantic more westerly which then leads to warmer temperatures across the eastern U.S.
- Negative Phase – The NAO is in this phase when the difference in pressure between the Azores High and the Subpolar Low is small and both systems are weak. This leads to a wavier jet stream and a blocking ridge over Greenland. This leads to warmer temperatures pushing north towards the North Pole over the Atlantic while colder temperatures move southward over the eastern U.S.
There’s another big, but lesser known, pattern that has major impacts on Mid-Latitude weather…the Madden-Julian Oscillation (MJO). The MJO can be a major contributor in wet weather patterns and help drive arctic air southward depending on it’s phase. You can read more on the MJO in this excellent blog by the folks at climate.gov.
My Bold Prediction
As always there will be periods of cold and snow and periods of sun and warmth. We are bound to experience some powerful storms that will bring rain, ice and heavy snow to the area, after all it’s Illinois. That said, here’s how I think our winter will look like when it’s all said an done. (Note the temperature forecast is for December, January and February while the snowfall forecast includes all snow from the first flake to the last.)
Temperature Outlook – Near to Below Average
(0° to 0.5° Below Average)
With this being a double-dip and weak to moderate La Niña winter, I think we will see greater influences from negative phases of the Arctic Oscillation which will ultimately bring colder than normal temperatures to the area. There will still be plenty of warm periods but I think these periods will be a little more transitory and by the end of February the temperature average will be slightly below average.
Precipitation Outlook – Wetter than average
(1.0″ to 1.5″ Above Average)
This portion of the forecast was largely based on typical La Niña expectations and seasonal model predictions. I think much of the upper Midwest including Central Illinois will see above average precipitation from December through February.
Snowfall Outlook – Near Average
(24.0″ to 28.0″ of Snow)
There’s no scientific basis for making a seasonal snowfall forecast so this is more for fun than anything, in fact, your guess here is as good as mine! That said with above average precipitation and near to below average snowfall I think will see some pretty snowy stretches. I also expect us to remain on the warm side of may storm systems, so while it looks to be a wet winter I think we’ll ultimately see near average snowfall.