The latest El Niño event officially ended in early June. But now, according to NOAA, there is a 75% chance that La Niña conditions will develop by the close of this summer.

El Niño and La Niña are opposite phases of a natural climate pattern known as the El Nino-Southern Oscillation or ENSO. A La Niña event is characterized by below average sea surface temperatures in the central and eastern equatorial Pacific. These cool waters influence the air temperature and affect the position of the jet stream.

In general, La Niña strengthens the polar jet and weakens the sub-tropical jet. This, in turn, affects weather patterns around the globe.

In the US, a La Niña event typically brings the southern states conditions that are warmer and dryer than normal. The northern tier, on the other hand, usually experiences below average temperatures with the northwest and Great Lakes region receiving above average precipitation. These impacts are most apparent during the fall and winter months.

La Niña also tends to reduce the wind shear over the tropical Atlantic. This provides favorable conditions for hurricane development.

The last La Niña event occurred in 2010-12.

Typical Winter La Nina jet stream pattern. Credit: NOAA