Peoria, Ill. (WMBD) — Warming sea surface temperatures across the Equatorial Pacific suggest that our rare triple dip La Niña is quickly coming to an end. With that trend expected to continue through Spring, it’s likely El Niño conditions will be in place by late Summer.
What is the El Niño Southern Oscillation (ENSO)?
ENSO consist of three phases, El Niño (positive phase), Neutral, and La Niña (negative phase). Each phase is determined by sea surface temperatures (SST) and how they compare to the long term average along with stronger atmospheric wind pattern over the equatorial Pacific.
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. and the Midwest.
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.
What Does This Mean For Severe Weather?
Historically La Niña conditions have lead to active severe weather seasons, particularly across parts of the south and Mississippi River Valley. While this hasn’t necessarily been the case locally, there have been some significant outbreaks that have taken place over the past three years, including tornado outbreaks in December and January. Recent studies have shown that as we transition from La Niña to El Niño tornado and hail events gradually trend down, particularly across the south.
This doesn’t mean it won’t be an active Spring severe weather season for Central Illinois, after all every year is different. But one can expect that as El Niño conditions develop the U.S. could expect to see a decrease in tornado and hail events over time.
If our current weather pattern were to persist into Spring, storm tracks would likely be somewhat favorable for a more active severe weather season for parts of the Midwest come March, April and May. In fact, the latest Spring Outlook from the Climate Prediction Center suggest that there’s an equal to likely chance that temperatures will be warmer than normal this Spring with a greater chance of above average precipitation. This could be an early sign that our upcoming severe weather season could be a bit more active compared to recent years.