La Niña is here!
Meteorologists have been expecting it for months, and now La Niña conditions have finally emerged in the tropical Pacific Ocean. A La Niña Advisory is currently in place with a 59% chance of continuing through April 2025. According to the Climate Prediction Center, the La Niña will be weak and eventually transition into a neutral phase.
What is La Niña and El Niño?
La Niña is one phase of the climate pattern called the El Niño Southern Oscillation (ENSO), which forms in the tropical Pacific. La Niña is the “cool” phase of ENSO, since the waters in this part of the Pacific are cooler than average. El Niño is the “warm” phase of ENSO, as the waters in the tropical Pacific are warmer than average. While the focus is typically on El Niño and La Niña, there is also a neutral phase. The neutral phase of ENSO basically means everything in this part of the Pacific Ocean is at or near their averages.
During La Niña, the phase we’re in now, the trade winds over the tropical Pacific Ocean are stronger than average, which creates upwelling. Upwelling brings up cooler water from deep in the ocean, causing water temperatures to drop. Also over this part of the ocean, the air sinks, leading to less rainfall. There is rising air and therefore more rain over places like Indonesia, however.
It’s the opposite during El Niño: The winds over the tropical Pacific Ocean are weaker, and so waters stay warmer. This leads to rising motion and more active, rainy weather over this part of the ocean, while sinking air leads to calm, drier weather in other places, such as Indonesia.
Walker Circulation
ENSO plays an important role in the Walker Circulation. The Walker Circulation is a cycle of rising and sinking air between the typically warmer waters of the western Pacific Ocean and the cooler waters of the eastern Pacific Ocean. It’s this Walker Circulation that helps drive the rising motion and, therefore, rain and storm activity.
What does this mean for the rest of winter?
This large circulation pattern has more of an impact on the United States in the winter, as the overall circulation can influence the location of the jet stream, a major driver for weather. So a La Niña winter for the United States (and parts of their neighbors to the north in Canada) typically features cooler weather from Alaska down to the northern Plains. It also means drier, warmer conditions from the desert southwest to the southeast. (See the map at the top of this post.)
In other parts of the world, especially for those near the western Pacific Ocean (in the Northern Hemisphere), meteorologists expect a more active, rainy trend through March.
Will La Niña impact summer and the Atlantic hurricane season?
La Niña in its current phase is not expected to last into the summer. The Climate Prediction Center anticipates the ENSO phase to become neutral sometime between March and May.
If La Niña were to remain in place for the upcoming Atlantic hurricane season, it would have had an influence on how active it could be. La Niña supports rising motion in the tropical Atlantic. And that would allow any forming tropical system to develop quickly. (Also, wind shear – the strong upper-level winds – are lower in the tropical Atlantic during La Niña. Wind shear can weaken or tear apart tropical systems, so lower wind shear would also allow for more easy tropical development.)
The forecast and outcome
The Climate Prediction Center issued a La Niña Watch during the summer of 2024 in anticipation of the development of this ENSO phase. A La Niña Watch gets issued when a La Niña is expected to develop within the next six months. At the time, meteorologists expected La Niña would develop during the summer, impacting the already active Atlantic hurricane season. But La Niña ended up not developing until December. The National Oceanic and Atmospheric Administration speculates that because the oceans have been running well above average for more than a year, it delayed the onset of the cool phase, La Niña.
Bottom line: After being expected for months, La Niña conditions have finally emerged in the tropical Pacific Ocean. Here’s what that means for our weather.
Via NOAA and National Weather Service
The post La Niña is here! Here’s what that means for our weather first appeared on EarthSky.
from EarthSky https://ift.tt/0x2yBqw
La Niña is here!
Meteorologists have been expecting it for months, and now La Niña conditions have finally emerged in the tropical Pacific Ocean. A La Niña Advisory is currently in place with a 59% chance of continuing through April 2025. According to the Climate Prediction Center, the La Niña will be weak and eventually transition into a neutral phase.
What is La Niña and El Niño?
La Niña is one phase of the climate pattern called the El Niño Southern Oscillation (ENSO), which forms in the tropical Pacific. La Niña is the “cool” phase of ENSO, since the waters in this part of the Pacific are cooler than average. El Niño is the “warm” phase of ENSO, as the waters in the tropical Pacific are warmer than average. While the focus is typically on El Niño and La Niña, there is also a neutral phase. The neutral phase of ENSO basically means everything in this part of the Pacific Ocean is at or near their averages.
During La Niña, the phase we’re in now, the trade winds over the tropical Pacific Ocean are stronger than average, which creates upwelling. Upwelling brings up cooler water from deep in the ocean, causing water temperatures to drop. Also over this part of the ocean, the air sinks, leading to less rainfall. There is rising air and therefore more rain over places like Indonesia, however.
It’s the opposite during El Niño: The winds over the tropical Pacific Ocean are weaker, and so waters stay warmer. This leads to rising motion and more active, rainy weather over this part of the ocean, while sinking air leads to calm, drier weather in other places, such as Indonesia.
Walker Circulation
ENSO plays an important role in the Walker Circulation. The Walker Circulation is a cycle of rising and sinking air between the typically warmer waters of the western Pacific Ocean and the cooler waters of the eastern Pacific Ocean. It’s this Walker Circulation that helps drive the rising motion and, therefore, rain and storm activity.
What does this mean for the rest of winter?
This large circulation pattern has more of an impact on the United States in the winter, as the overall circulation can influence the location of the jet stream, a major driver for weather. So a La Niña winter for the United States (and parts of their neighbors to the north in Canada) typically features cooler weather from Alaska down to the northern Plains. It also means drier, warmer conditions from the desert southwest to the southeast. (See the map at the top of this post.)
In other parts of the world, especially for those near the western Pacific Ocean (in the Northern Hemisphere), meteorologists expect a more active, rainy trend through March.
Will La Niña impact summer and the Atlantic hurricane season?
La Niña in its current phase is not expected to last into the summer. The Climate Prediction Center anticipates the ENSO phase to become neutral sometime between March and May.
If La Niña were to remain in place for the upcoming Atlantic hurricane season, it would have had an influence on how active it could be. La Niña supports rising motion in the tropical Atlantic. And that would allow any forming tropical system to develop quickly. (Also, wind shear – the strong upper-level winds – are lower in the tropical Atlantic during La Niña. Wind shear can weaken or tear apart tropical systems, so lower wind shear would also allow for more easy tropical development.)
The forecast and outcome
The Climate Prediction Center issued a La Niña Watch during the summer of 2024 in anticipation of the development of this ENSO phase. A La Niña Watch gets issued when a La Niña is expected to develop within the next six months. At the time, meteorologists expected La Niña would develop during the summer, impacting the already active Atlantic hurricane season. But La Niña ended up not developing until December. The National Oceanic and Atmospheric Administration speculates that because the oceans have been running well above average for more than a year, it delayed the onset of the cool phase, La Niña.
Bottom line: After being expected for months, La Niña conditions have finally emerged in the tropical Pacific Ocean. Here’s what that means for our weather.
Via NOAA and National Weather Service
The post La Niña is here! Here’s what that means for our weather first appeared on EarthSky.
from EarthSky https://ift.tt/0x2yBqw
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