Winter’s Warm Embrace: The El Niño Effect
As the winter season approaches, meteorologists consistently encounter a similar set of questions each year: How cold will it be? When will it snow? How much snow will there be? This winter is a moderate/strong El Niño and lasts into spring. But what does that mean?
What is El Niño? El Niño refers to part of the oscillating pattern involving sea surface temperatures in the central and eastern Pacific Ocean. The El Niño “phase” of the oscillation is characterized by the periodic warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean, causing suppression of cold water off the coast of South America. The El Niño pattern is linked to an atmospheric circulation known as the Southern Oscillation. This involves a slowdown of the usual west-to-east wind pattern in the tropical Pacific, leading to a buildup of warmer water and creating a warming feedback loop. As a result, a high-pressure system develops over the eastern Pacific Ocean.
How is the strength of an El Niño determined? The Climate Prediction Center assesses and forecasts the intensity of this oscillation, primarily relying on the Oceanic Niño Index (ONI). The ONI is a metric calculated as a 3-month running average of sea surface temperature anomalies (variance from the average) in the central equatorial Pacific Ocean.
How does an El Niño influence winter weather in the continental U.S.? Generally, the warmer surface water in the Eastern Pacific tends to push colder air farther north. likely resulting in warmer-than-usual temperatures in the Northern and Eastern U.S., especially early in the winter months.
Some general trends associated with El Niño events include:
1. Warmer and Drier Conditions in the Northern States: El Niño tends to bring milder temperatures and reduced precipitation to the northern part of the United States. This can result in a drier and warmer winter than usual in states like the northern Plains and the Midwest.
2. Wetter Conditions in the Southern States: Conversely, the southern part of the U.S., particularly the southern Plains and the Southeast, often experiences increased precipitation during El Niño events. This can lead to above-average rainfall and the potential for flooding in some areas.
3. Warmer Temperatures in the East: The eastern part of the country, including the Northeast, may experience milder winter temperatures during El Niño events. This can lead to a reduction in the frequency and severity of cold outbreaks.
In terms of snow, many other weekly and monthly patterns play a large role in how waves of air move and storm patterns form. Generally, milder temperatures during El Niño events are associated with a lower likelihood of snowfall, especially in the Midwest, Northeast, and Mid-Atlantic states.
It’s important to note that while El Niño provides a general framework for understanding potential winter weather patterns, other atmospheric and oceanic factors also play a role.