Everything is connected. The surface temperature of the tropical Pacific Ocean can affect weather patterns all over the globe. When that temperature cools as part of a La Niña pattern, the US can expect colder and rainier conditions in the north with warmer and drier conditions across the southern states. That can have an impact on everything from snow days to heating bills. Let's dive into what's going on with a predicted La Niña event this winter.
Meet ENSO
If you hang around weather people, you might encounter the shorthand phrase ENSO. That stands for El Niño-Southern Oscillation.
"ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe," the National Oceanic and Atmospheric Administration explains.
ENSO encompasses both La Niña (the girl) and El Niño (the boy), but there's also a third phase: neutral. ENSO is a natural cycle that moves between these states. We've been in a neutral phase, according to NOAA, but scientists expect a weak La Niña to develop this fall.
What is La Niña?
La Niña and El Niño are naturally occurring climate patterns. A La Niña event refers to the cooling of ocean surface temperatures in a particular region of the Pacific Ocean, the central and east-central equatorial areas.
"Typically, a La Niña is preceded by a buildup of cooler-than-normal subsurface waters in the tropical Pacific," NOAA says. "Then, easterly trade winds strengthen, cold upwelling off the west coast of South America and along the equator intensifies, and sea-surface temperatures drop below normal." That's the recipe for La Niña.
Jet streams are high-level air currents that move from west to east. Jet stream winds help direct storm paths and also act as a boundary between warmer (to the south) and colder (to the north) air masses.
"The location of the jet, and hence also the boundary, has a strong influence on temperatures down at ground level," climate scientist Tim Woollings wrote in a NOAA explainer.
La Niña pushes the jet stream -- and the storms it directs -- to the north. La Niña rolls around every few years and can last for a couple years. The impacts on weather are most pronounced during the winter months. If it kicks in this year, then look for wetter conditions in the Pacific Northwest with hotter than normal temperatures across the southern US.
What is El Niño?
A winter El Niño pattern typically bring wetter and colder conditions in the southern US while the northern areas are warmer. Forecasters don't expect El Niño for winter 2024.
NOAAEl Niño is the flip side of La Niña. Recent extreme heat conditions can be traced to the climate crisis. El Niño -- the part of the ENSO cycle when equatorial Pacific Ocean surface temperatures are warmer than average -- also played a role. An El Niño event usually brings wetter conditions to the southern US with warmer and drier conditions to the north. El Niño typically lasts for a shorter time than La Niña.
Will La Niña happen in 2024?
The National Weather Service issued a seasonal temperature outlook for November through January showing above-normal temperatures for the southern and eastern regions of the US.
NOAA/National Weather ServiceThe National Weather Service forecasts a 60% chance of La Niña developing sometime through November. It's expected to be a weak event if it forms.
Historically, La Niña events that occur this late in the year tend to be weak.
"The strength of an ENSO event, as gauged by its sea surface temperature departures, matters because stronger events change the atmospheric circulation more consistently, leading to more consistent impacts on temperature, rainfall and other patterns," research scientist Emily Becker wrote in an October ENSO update for NOAA. That leaves room for forecasts to shift as we move through the end of the year.
The National Weather Service's seasonal precipitation outlook for the rest of 2024 shows a chance for wetter conditions up north and drier conditions down south.
NOAA/National Weather ServiceThe NWS Climate Prediction Center issued seasonal outlooks for November through January showing a likelihood for above-normal temperatures for the southern and eastern regions of the US. Look for below-normal precipitation stretching coast to coast across the south. The northern parts of the country could have above-normal precipitation. That's in line with expectations for a weak La Niña.
We're currently in a La Niña watch. Expect an official ENSO update in mid-November. By that point, we may have a better idea of whether you should invest in a new umbrella, get warmer workout gear or plan to water your lawn more often this winter.