ENSO Blog

La Niña continues in the tropical Pacific, but it has weakened recently, and forecasters estimate about a 60% chance of a transition to neutral conditions in the late spring. Looking farther out into the fall of 2021, El Niño is unlikely to develop, and the chances of La Niña and neutral are similar. Migratory birds The February 2021 average sea surface temperature in the Niño3.4 region—our primary ENSO monitoring index—was just about the same as January, at about 1.0°C cooler than the 1991–2020 average, according to the ERSSTv5 dataset. (ICYMI: I covered the shift to the 1991–2020 average last month.) This comfortably exceeds the La Niña threshold of 0.5°C cooler than average. …   Read article

We are rapidly approaching the end of the meteorological winter, and it has been quite a finish for much of the United States, especially for those who have suffered the devastating effects of recent extreme cold. As discussed on this blog, we have been in the grips of a healthy La Niña, but the weather outside of the tropics often hasn’t behaved as we would expect for La Niña, even before this period of extreme cold and winter storms. In this post, we’ll investigate what was going on for the first two-thirds of this winter. Feeling the pressure As Emily mentioned back in January, the early winter temperature pattern over North America looked more like a typical El Niño than what we wo…   Read article

La Niña is still here, but forecasters estimate about a 60% chance that neutral conditions will return this spring. By the fall, the chance that La Niña will return is approximately equal to the chance that it will not. Let’s take a stroll around ENSO’s eclectic bookshelf and see what we can learn Romance novels The temperature of the ocean surface in the Niño 3.4 region of the tropical Pacific, our primary El Niño/Southern Oscillation (ENSO) measurement, was just about 1.0°C (1.9°F) below the long-term average in January, according to the ERSSTv5 dataset. As of this month, the long-term average is calculated over 1991–2020. (More on this page-turner later!) Of course, ENSO woul…   Read article

The POLAR VORTEX is coming!!!!!  That’s the ALL CAPS message these days in various news articles thanks due to the sudden stratospheric warming that occurred on January 5, 2021. We’re going to take a deeper look at the polar vortex and possible interactions with our ongoing La Niña. But, to recap previous articles on this blog: — The Polar Vortex doesn’t just appear randomly. The polar vortexes (more than one!) are a regular feature in the atmosphere, spinning away around the poles in both the Northern and Southern Hemispheres. — There is the stratospheric polar vortex, which is located in the layer that is 5-30 miles above Earth’s surface and only ap…   Read article

There’s a 95% chance that La Niña will continue through the winter and a 55% chance the tropical Pacific will transition to neutral conditions by the spring. After that, the picture is less clear. Certainly less clear than the waters of the tropical Pacific... Tahiti Speaking of, let’s take the temperature of the tropical Pacific Ocean. The December 2020 average sea surface temperature in our primary monitoring region, Niño 3.4, was 1.2° Celsius (2.16˚ Fahrenheit) cooler than the long-term (1986-2015) average, according to the ERSSTv5 dataset. This is comfortably within the La Niña boundary of more than 0.5°C cooler than average. The cooler-than-average wedge of La Niña is clear in …   Read article