All across the state of California, millions of Americans are feeling the negative side effects of the statewide drought. This drought is often attributed to climate change, which is also the most compelling reason as to why this winter is projected to be a La Niña.
The La Niña, also known as El Viejo, is the opposite of an El Niño, or cold event. When water cools across the Equatorial Pacific at random times because of variations in the weather pattern, it is considered a La Niña. El Niño is when there is periodical warming in sea surface temperatures across the central Equatorial Pacific. During the 2015 to 2016 year, an El Niño dominated the weather cycle, leading it to be abnormally warm. As temperatures remain close to average now in the following year, it is called La Nada, translating to neutral weather conditions.
During a La Niña in the U.S., the temperature is warmer than normal in the Southeast and cooler than normal in the Northwest. Changes like this tend to last nine to twelve months and events occur on average every two to seven years. Typically, El Niño occurs more frequently than La Niña.
La Niña seems to influence the northern jet stream by pushing moisture across the Northern layer of the U.S. Frequently with this it causes the Southern jet stream to weaken, diminishing the storm threat there.
The transition in temperatures can also have an impact on the global climate, bringing heavy rainfall to Indonesia, the Philippines, Northern Australia and Southern Africa. In the U.S., continual warm and dry conditions for Southern California usually result in drought conditions. The weather pattern may also have an influence on the Southwest with an increase in drought problems.
El Niño and La Niña are opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the adjustments in temperature between the ocean and atmosphere in the east-central Equatorial Pacific.
The common traits of the beginning of an El Niño include mild winter temperatures over Western Canada and North Western USA, above average precipitation in the Gulf Coast, and a drier than average period in Ohio and Pacific Northwest. Differing from this, the La Niña also has familiar qualities to it. This includes stronger winds along the equatorial region, especially in the Pacific, along with reduced convection in the Pacific leading to a weaker jet stream. Temperatures are found to be above average in the Southeast and below average in the Northwest, and with conditions that are more favourable for hurricanes in the Caribbean and central Atlantic area, also resulting in greater occurrences of tornadoes in the U.S. with states already vulnerable to them.
By Katherine McCormick