El Niño Southern Oscillation (ENSO)
Many of us have heard the term “El Niño” at some point in our lives. But you may not know how significant a role El Niño plays with our weather patterns in the continental U.S..
Many global elements affect weather patterns. Among the most significant are global ocean currents and associated cycles of warming and cooling ocean water temperature. There are several such ocean water temperature cycles. One that is highly influential to weather across the U.S. is the El Niño Southern Oscillation (ENSO). ENSO pertains to an area of the central and eastern Pacific Ocean near the equator where the ocean water temperature fluctuates by several degrees above and below average every few years.
When these ocean water temperatures are warmer than normal, we are in the “El Niño” phase of the ENSO cycle. When they are cooler than normal, we are in the “La Niña” phase. At any given time, ENSO may be in either an El Niño, La Niña or “neutral” (close to normal). These phases tend to persist for a few years at a time with small intermediate fluctuations in between.
ENSO has been long known to effect weather patterns in the northern hemisphere. In the continental U.S., the effect of ENSO is most prevalent during the winter months. It can also dramatically affect the Atlantic hurricane season.
U.S. Weather During El Niño:
When ENSO is in an El Niño phase during the winter, storm systems tend to impact the southern states with above normal precipitation from southern California eastward to Texas and the Gulf states. Meanwhile, the northern and central states tend to be drier than normal with fewer storms and mild temperatures during an El Niño phase. Additionally, when El Niño is present during the summer and fall, the Atlantic Ocean tends to have below normal tropical storm and hurricane activity. Two of the strongest El Niño years in recent history were in 1997 and 2015. In both years, there was below average tropical storm and hurricane activity in the Atlantic. This is especially true in 1997 with only 7 named storms, which is half of the 1990-2020 annual average.
U.S. Weather During La Niña:
When ENSO is in the La Niña phase during the winter, the northern and central states tend to be stormy with above normal precipitation from the Pacific Northwest to the Great Lakes. La Niña winters also tend to be more active for snowstorms over areas like Washington D.C., New York, and New England. Meanwhile, the southern states are typically warmer and drier than normal during a La Niña phase. Additionally, tropical storm and hurricane activity in the Atlantic is typically at or above normal when ENSO is neutral or in a La Niña phase. The most active hurricane seasons we’ve had in the past few decades were in 2005 with 27 named storms, and more recently in 2020 with a record 30 named storms. ENSO was near neutral during the 2005 season and in a La Niña phase in 2020.
Current Phase of ENSO and Outlook:
The National Oceanic and Atmospheric Administration (NOAA) is among several organizations which study and monitor ENSO. They have data that goes back several decades. According to the Climate Prediction Center, ENSO has been predominantly in the La Niña phase since summer of 2020. This La Niña phase coincides with the active hurricane seasons of 2020 and 2021, and a rather active winter storm pattern in early 2022 over the central and northern states.
While the correlation between ENSO and U.S. weather patterns is often strong, predicting phases of ENSO and its effects on our weather patterns is not so simple. ENSO is an irregular cycle and difficult to predict more than 3-6 months in advance. Despite the challenges, forecasting ENSO and other similar phenomenon that effect weather and climate is very important. Efforts to learn more about them are ongoing and will continue for years to come.
The Climate Prediction Service issues regular updates and forecasts of ENSO. As of March 2022, ENSO was forecast to remain in a La Niña phase through Spring 2022, and transition to neutral by July 2022. Find out more about the El Niño Southern Oscillation (ENSO) here.
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