Often when discussing winter weather conditions we hear the terms El Niño and La Niña tossed around. But what do either of them actually mean, and how will they impact snowfall and conditions on the mountain? We have been bringing you a lot of winter weather forecasts this year, from both the NOAA and the Old Farmer's Almanac, so in hopes of further clarifying what is inherently loaded with technical jargon, we have set out to answer the above question for you.
What are El Niño and La Niña?
El Niño and La Niña are opposite phases of the El Niño – Southern Oscillation, also known as the ENSO cycle. The ENSO cycle is a tongue-twister of scientific jargon that in layman’s terms describes the changes in the temperature difference between the ocean and atmosphere in the east-central Pacific. Of these two phases, La Niña is considered the colder phase, while El Niño is thought of as the warmer phase. Both phases of this cycles are key in understanding weather forecasts because fluctuation in normal surface temperature has an incredibly large impact on the global climate.
Both phases of the cycles typically last between 9-12 months, however, because they are reliant on global weather patterns, some individual phases have been prolonged for as long as multiple years. It is also key to note, that while La Niña and El Niño are opposite phases of a cycle, we are not always technically in one or the other.
That is because of the often overlooked “neutral” phase, in which temperature differences between the surface and atmosphere are negligible. The El Niño and La Niña phases tend to occur on average every two to seven years, however, El Niño has historically occurred much more often than La Niña.
Understanding El Niño
The classification of an El Niño season dates all the way back to the early 1600s when fishermen noticed unusually warm water in the Pacific. The phrase itself translates to “little boy” or “Christ child” and comes from the fact that it was first noticed around December when the El Niño phase typically begins.
As mentioned, El Niño refers to the warmer of the two phases and is a result of a substantial warming of the surface temperature in the Pacific Ocean. El Niño typically develops around the same time that we slide into winter in the Northern Hemisphere.
What happens is that the warmer surface temperature of the ocean creates rising motion in the atmosphere over the Pacific (and a sinking motion in the atmosphere over the Atlantic) which shifts the jet stream south and subsequently causes greater storms and increased rain over the southern portion of the country. This phenomenon gets reflected by warmer-than-average atmospheric temperatures over the western and northern portions of North America. So, during an El Niño season, it can be expected that southern parts of the country will see an increase in precipitation, where much of the northern half of the country will see less precipitation and generally warmer weather.
Understanding La Niña
The La Niña phase is the exact opposite of El Niño. A La Niña phase is classified by colder than average water temperatures in the east-central Pacific which creates a sinking motion with the atmosphere. This sinking motion in the atmosphere over the Pacific also brings with it a rising motion in the atmosphere over the Atlantic, and thus shifts the jet stream north. When the jet stream is shifted north, the likelihood for intense storms and increased precipitation in the northern portion of the country is increased. Likewise, the Pacific Northwest will see much colder temperatures, while the southeastern portion of the country will be warmer.
Understanding the Winter Ahead
This coming winter season has been forecasted to be an El Niño year. This means that warmer than average temperatures can be expected throughout the country, and the northern part of the country will likely see a drier season, while the southeastern portion of the country will see an increase in precipitation. All the same, don't fret just yet. El Niño phases are far more common than La Niña, and while they are historically accurate in predicting overall weather patterns, they don't dictate localized weather. It's still going to snow.
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