I’ll admit, February is my least favorite month. The winter blues set in, and find myself getting restless in anticipation for the warmer months ahead. The good news is that dismal February is only 28 days long! This winter, and especially lately, we have been seeing the effects of a mild La Niña weather pattern. According to the National Ocean Service, a La Niña, meaning “the little girl” in Spanish, is the complementary phase to El Niño, “the little boy”. Both are a part of the El Niño-Southern Oscillation (ENSO) cycle, each event lasting an average of nine to twelve months. Their frequency is irregular, but El Niño and La Niña events take place on average every two to seven years, with El Niño occurring more frequently. These complex weather patterns are due to variations in ocean temperatures in the Pacific Ocean, along the equator.
If these weather patterns are due to events happening in the Equatorial Pacific, why should we care? It turns out that warmer or colder than average ocean temperatures (even just fluctuations of +/- 0.5 to 2 degrees Celsius) in one part of the world can influence weather around the globe (NOAA)! The fluctuations above or below “normal” are seemingly minuscule, but cause a cascade of weather events that we can see here in the Midwest.
During normal conditions, trade winds blow from east to west and push warm surface waters towards Asia, pooling the warmth in the Western Pacific. Sometimes the trade winds become winded (pun intended) and weaken, and all of that warm surface water is pushed back to the east, pooling instead along Mexico, Central and South America. When this happens, the typically cooler upwelling along the coast of South America is reduced – this is El Niño. El Niño features a strong jet stream and storm track across the southern part of the US, and shows itself in the Midwest by bringing us warmer, drier winters. When the weak trade winds finally pick up again, they push the warm surface water back west with even more force than normal. The cool upwellings resurface in the Eastern Pacific, and cause unusually cold conditions in this area – this is La Niña. La Niña positions the jet stream over the Great Lakes more frequently, leading to storm activity. It brings potential drought to the southern US, with cooler temperatures and above average precipitation to the northern US. According to the Climate Prediction Center, La Niña conditions in 2018 are expected to decay rapidly and transition to an ENSO-neutral state during spring, which will persist through the summer months.
All that to say – we are experiencing the effects of La Niña in our backyard, especially today! On my way to the office this morning, I stopped to snap a picture of the unusually high water levels in Forked Creek, located in the south part of Will County, close to the county line (photo below). It’s fun to give a little explanation to something we’re seeing firsthand, helping us to plan ahead and prepare for the upcoming months.