Peoria, Ill. (WMBD) — Temperatures are dropping, and winter is just around the corner. In this article I’ll discuss the various factors that will impact our upcoming winter season and layout my prediction for the next 3 months.
Outlook Summary
- Strong El Niño is expected this winter
- Near to above average temperatures expected
- Near to below average precipitation expected
- Below average snowfall expected
Average Winter Conditions for Peoria (December, January & February)
- Seasonal Mean Temperature – 28.8°
- Average Precipitation – 6.25″
- Average Snowfall – 26.2″
After three consecutive winters with La Niña conditions across the equatorial Pacific, a moderate to strong El Niño has formed and could help shape this upcoming winter. You can read more about El Niño and the other teleconnections that shape our winter season further into the article.
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 Above Average
(0° to 1.5° Above Average)
This El Niño is expected to be a strong El Niño event and historically these strong El Niños have lead to warmer than normal conditions across the Midwest. While every El Niño is different, and there are some signs that this season will be a little different than past strong El Niño events, I still think that temperatures will end up warmer than average.
I think this seasonal forecast from the European model has the right idea in that our December is likely to be warmer than average but we see bigger shots of cold in January and early February. While it’s possible we see below average temperatures in January and early February, it may not be enough to offset our warm December.
Precipitation Outlook – Near to Below Average
(0″ to 1.5″ Below Average)
Largely based on the performance of past El Niño events, I think this winter will end up with less precipitation than normal. It’s not unusual for parts of the region, particularly western parts of Illinois, to see near to above average precipitation.
Snowfall Outlook – Below Average
(18.0″ to 24.0″ of Snow)
There’s no scientific basis for making a seasonal snowfall forecast but we can look back at past El Niño events to get a sense of what has happened before. When we look back at the 10 strongest El Niño events we find that much of the Midwest sees well below average snowfall (image below). Since this El Niño may not behave like a typical strong El Niño, we’ll likely encounter some snowy stretches this winter, but ultimately I think we end up below average.
Breakdown of Various Teleconnections
The following teleconnections will help shape our upcoming winter season. Here is what they are and how they influence our weather…
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.
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.
