The current El Niño event, which began in March, is continuing to evolve and strengthen.
According to NOAA, this El Niño has a 90% chance of lasting through the autumn and an 85% chance of sticking around until next winter. While it is more difficult to predict the strength of an El Niño than its duration, the current forecast is calling for a “strong” event, which will likely impact temperature and precipitation patterns around the country.
El Niño is the warm phase of the larger El Niño-Southern Oscillation, known as ENSO. It is a naturally occurring oceanic-atmospheric phenomenon that influences weather around the globe. Its main indicators are warmer than average sea surface temperatures in the eastern and central Pacific Ocean near the equator as well as a weakening of the Trade Winds.
Impacts from a moderate to strong El Niño are usually most noticeable during the autumn and winter months. This is because winter weather is governed more by large scale processes – like nor’easters – than summer weather. In the US, these impacts include wetter than average conditions from southern California to parts of the east coast and for many of the southern states in-between. Drier than average conditions tend to settle over parts of the Ohio Valley, Great Lakes, and northern Rockies. In terms of temperature, the southwest and southern plains tend to be cooler than average while the northern tier of the country is generally warmer than average.
Although these are considered the typical regional impacts of an El Niño event, they are not guaranteed to happen. Every El Niño is different. It is also important to remember that El Niño is not the only driver of atmospheric circulation. When present, it works in concert with other major players such as daily variability and the influence of climate change.
During the summer months, impacts from El Niño in the US tend to be fairly weak. That said, its presence typically dampens the development of storms during the Atlantic Hurricane Season. As the water in the Pacific warms, it generates convection and creates westerly winds in the upper atmosphere over the Gulf of Mexico, Caribbean Sea, and Western Atlantic. This wind shear tends to limit the strengthening of any tropical cyclones in the area.
Coming on the heels of a record warm 2014, this El Niño event could help push 2015’s average global temperature to even higher record-breaking levels. Year to date, according to NOAA, the first four months of 2015 have already been the warmest ever recorded.
Typical Winter El Niño Pattern for US. Credit: NOAA