NOAA scientists are officially declaring an El Niño event is underway in the eastern tropical Pacific Ocean. The agency anticipates that this El Niño is likely to become strong by the fall and possibly very strong by the winter. There is the potential for this El Niño event to become one of the strongest in modern record.A very strong El Niño does make a wet winter more likely for California, but it doesn’t guarantee that’s how things will go this year. Historically, outcomes are mixed. As NOAA explicitly highlights in its monthly update, “no two El Niño events are the same”. That’s because El Niño is only one climate driver. Its impacts depend on a combination of other large-scale and small-scale atmospheric patterns. Below is a deep dive into what El Niño is, how it’s classified, the impacts of past very strong events in Northern California and where the uncertainties lie this year. What is El Niño?El Niño is a cyclical, long-term global weather phenomenon marked by warmer than normal ocean temperatures. It is not a single “storm” or even a “series of storms.”An El Niño pattern emerges when water temperatures in the eastern tropical Pacific Ocean are warmer than normal. At the same time, tropical trade winds get weaker. These changes in the wind and water shift where clusters of thunderstorms form. Shifts like this can ripple through the atmosphere and affect temperature and precipitation patterns in North America but altering the flow of the jet stream. For California, El Niño’s influence tends to be most significant between late fall and winter. Measuring El NiñoScientists track El Niño intensity by measuring ocean temperature anomalies in the central and eastern tropical Pacific. This region is called Niño 3.4.El Niño events vary in strength and NOAA says that they often last nine to 12 months, though some last longer. When the temperature anomaly is .5 to .9 degrees Celsius for at least three months, a “weak” El Niño is occurring. This is the status of this year’s newly declared El Niño event. NOAA says water temperatures are averaging .7 degrees warmer than normal. A “moderate” El Niño is marked by an anomaly of 1 to 1.4 degrees Celsius. An El Niño event is considered “strong” between 1.5 and 1.9 degrees Celsius. Anything above 2 degrees Celsius is “very strong.” While many outlets have been using the term “super El Niño” to describe this year’s event, this is not a term that is widely accepted among scientists. NOAA uses “very strong” to describe the most potent El Niño events. The KCRA3 weather team follows this standard as well.How strong could this El Niño event be?This El Niño event has only just emerged, but it is expected to strengthen significantly over the next several months. NOAA forecasters say that “strong” El Niño conditions are likely by the end of the summer. A “very strong” El Niño could develop late this fall or early in the winter. According to NOAA’s outlook released on June 11, there is a 63% chance of a very strong El Niño forming. It is possible that this year’s event could become one of the strongest since 1950, when modern record keeping began. Note that there can be months of delay between the emergence of an El Niño and notable impacts to global weather patterns. What happened in Northern California during previous very strong El Niño events? Since 1950, four “very strong” El Niño events have occurred. The most powerful in that time came during the winter of 1982-1983. Events in 1997-1998, 2015-2016 and 1991-1992 rank second through fourth. In general, the stronger an El Niño event is, the more the scales get tipped towards certain expected impacts for North America. But those impacts can still vary greatly from event to event. The 1983 and 1998 water years were very wet in Northern California. Sacramento, Stockton and Modesto each about doubled their typical rainfall. Both years had damaging flooding. Snowfall was well above normal.But the water year of 1992 looked very different. Northern California was relatively dry. Snowfall was just 66% of normal at the UC Berkeley Central Sierra Snow Lab. For comparison, this past winter snowfall at the lab site was 85% of normal.A “very strong” El Niño pattern does tip the odds in favor of a wet winter in this area, but it is not a guarantee.Even then, it will be the day-to-day weather and timing of any strong storms that determine the overall course of this coming winter. These are details that can only start to come into view a couple of weeks before they happen.Why do El Niño impacts vary?The winters of 1983 and 1998 have made El Niño synonymous with powerful storms and damaging floods for Northern California. Because of this, El Niño now makes a lot of headlines and it grabs a lot of attention on social media platforms. But it is important to remember that El Niño is one major climate driver, but it is not the only one. The Pacific-North American pattern (PNA) influences where troughs of low pressure and ridges of high pressure set up. The Arctic Oscillation affects the shape of the jet stream and how easily arctic air can drop into the lower latitudes. The Pacific Decadal Oscillation (PDO) is like El Niño but on a much longer timescale and the area of focus is the north Pacific Ocean. These so-called “teleconnections” combine with El Niño to drive the setup for a winter season. Long range forecast experts at NOAA consider all of these factors when creating a seasonal temperature and precipitation outlook. Short term weather features ultimately have the final say. Days or weeks of a stubborn area of high pressure can block Pacific storms from hitting California. A series of atmospheric river storms can turn an otherwise dry season into one with dangerous flooding. Forecast models can’t highlight these kinds of details more than a couple of weeks out. Even then, California’s diverse geography and microclimates ensure that impacts will vary.How should Northern Californians prepare?El Niño does not guarantee a wet or damaging winter in Northern California, but it is a good reason to get ready for the wet season ahead of time.That means the usual tasks like clearing gutters and drains at the end of the summer, checking the flood risk around your home, restocking emergency supplies, and making sure you can receive weather alerts quickly. Take a few minutes and sign up for your county or city’s emergency alert program.Download the KCRA 3 app for the latest, trusted information from our meteorologists and our breaking news alerts. For people in the Foothills, burn scar areas, or other flood-prone locations, it is also a good time to review evacuation plans before storm season ramps up.The bigger picture is this: El Niño may raise the odds of certain impacts, but the actual risks to Northern California will depend on the day-to-day weather patterns that take shape later this fall and winter.See more coverage of top California stories here | Subscribe to our morning newsletter | Find us on YouTube here and subscribe to our channelPHNjcmlwdCB0eXBlPSJ0ZXh0L2phdmFzY3JpcHQiPiFmdW5jdGlvbigpeyJ1c2Ugc3RyaWN0Ijt3aW5kb3cuYWRkRXZlbnRMaXN0ZW5lcigibWVzc2FnZSIsKGZ1bmN0aW9uKGUpe2lmKHZvaWQgMCE9PWUuZGF0YVsiZGF0YXdyYXBwZXItaGVpZ2h0Il0pe3ZhciB0PWRvY3VtZW50LnF1ZXJ5U2VsZWN0b3JBbGwoImlmcmFtZSIpO2Zvcih2YXIgYSBpbiBlLmRhdGFbImRhdGF3cmFwcGVyLWhlaWdodCJdKWZvcih2YXIgcj0wO3I8dC5sZW5ndGg7cisrKXtpZih0W3JdLmNvbnRlbnRXaW5kb3c9PT1lLnNvdXJjZSl0W3JdLnN0eWxlLmhlaWdodD1lLmRhdGFbImRhdGF3cmFwcGVyLWhlaWdodCJdW2FdKyJweCJ9fX0pKX0oKTs8L3NjcmlwdD4=
NOAA scientists are officially declaring an El Niño event is underway in the eastern tropical Pacific Ocean.
The agency anticipates that this El Niño is likely to become strong by the fall and possibly very strong by the winter. There is the potential for this El Niño event to become one of the strongest in modern record.
A very strong El Niño does make a wet winter more likely for California, but it doesn’t guarantee that’s how things will go this year. Historically, outcomes are mixed.
As NOAA explicitly highlights in its monthly update, “no two El Niño events are the same”. That’s because El Niño is only one climate driver. Its impacts depend on a combination of other large-scale and small-scale atmospheric patterns.
Below is a deep dive into what El Niño is, how it’s classified, the impacts of past very strong events in Northern California and where the uncertainties lie this year.
What is El Niño?
El Niño is a cyclical, long-term global weather phenomenon marked by warmer than normal ocean temperatures. It is not a single “storm” or even a “series of storms.”
An El Niño pattern emerges when water temperatures in the eastern tropical Pacific Ocean are warmer than normal. At the same time, tropical trade winds get weaker.
These changes in the wind and water shift where clusters of thunderstorms form. Shifts like this can ripple through the atmosphere and affect temperature and precipitation patterns in North America but altering the flow of the jet stream.
For California, El Niño’s influence tends to be most significant between late fall and winter.
Measuring El Niño
Scientists track El Niño intensity by measuring ocean temperature anomalies in the central and eastern tropical Pacific. This region is called Niño 3.4.
Hearst Owned
Scientists track El Niño and La Niña patterns by monitoring ocean temperatures in a specific section of the tropical eastern Pacific. This region is known as “Niño 3.4”
El Niño events vary in strength and NOAA says that they often last nine to 12 months, though some last longer.
When the temperature anomaly is .5 to .9 degrees Celsius for at least three months, a “weak” El Niño is occurring. This is the status of this year’s newly declared El Niño event. NOAA says water temperatures are averaging .7 degrees warmer than normal.
Hearst Owned
The strength of an El Niño event is defined by ocean temperature anomalies. The warmer temperatures are compared to normal, the stronger the El Niño pattern is.
A “moderate” El Niño is marked by an anomaly of 1 to 1.4 degrees Celsius. An El Niño event is considered “strong” between 1.5 and 1.9 degrees Celsius.
Anything above 2 degrees Celsius is “very strong.” While many outlets have been using the term “super El Niño” to describe this year’s event, this is not a term that is widely accepted among scientists. NOAA uses “very strong” to describe the most potent El Niño events. The KCRA3 weather team follows this standard as well.
How strong could this El Niño event be?
This El Niño event has only just emerged, but it is expected to strengthen significantly over the next several months.
NOAA forecasters say that “strong” El Niño conditions are likely by the end of the summer. A “very strong” El Niño could develop late this fall or early in the winter.
According to NOAA’s outlook released on June 11, there is a 63% chance of a very strong El Niño forming. It is possible that this year’s event could become one of the strongest since 1950, when modern record keeping began.
Note that there can be months of delay between the emergence of an El Niño and notable impacts to global weather patterns.
What happened in Northern California during previous very strong El Niño events?
Since 1950, four “very strong” El Niño events have occurred. The most powerful in that time came during the winter of 1982-1983. Events in 1997-1998, 2015-2016 and 1991-1992 rank second through fourth.
Hearst Owned
The strongest El Niño in modern recorded history occurred during the winter of 1982-83.
In general, the stronger an El Niño event is, the more the scales get tipped towards certain expected impacts for North America. But those impacts can still vary greatly from event to event.
The 1983 and 1998 water years were very wet in Northern California. Sacramento, Stockton and Modesto each about doubled their typical rainfall. Both years had damaging flooding. Snowfall was well above normal.
Hearst Owned
These maps show winter precipitation anomalies during three of the four strongest El Niño patterns on record. The winters of 1983 and 1998 were part of exceptionally wet water years for California. However, the winter of 1992 was dry for the northern half of the state.
But the water year of 1992 looked very different. Northern California was relatively dry. Snowfall was just 66% of normal at the UC Berkeley Central Sierra Snow Lab. For comparison, this past winter snowfall at the lab site was 85% of normal.
A “very strong” El Niño pattern does tip the odds in favor of a wet winter in this area, but it is not a guarantee.
Even then, it will be the day-to-day weather and timing of any strong storms that determine the overall course of this coming winter. These are details that can only start to come into view a couple of weeks before they happen.
Why do El Niño impacts vary?
The winters of 1983 and 1998 have made El Niño synonymous with powerful storms and damaging floods for Northern California.
Because of this, El Niño now makes a lot of headlines and it grabs a lot of attention on social media platforms.
But it is important to remember that El Niño is one major climate driver, but it is not the only one.
The Pacific-North American pattern (PNA) influences where troughs of low pressure and ridges of high pressure set up. The Arctic Oscillation affects the shape of the jet stream and how easily arctic air can drop into the lower latitudes. The Pacific Decadal Oscillation (PDO) is like El Niño but on a much longer timescale and the area of focus is the north Pacific Ocean.
These so-called “teleconnections” combine with El Niño to drive the setup for a winter season. Long range forecast experts at NOAA consider all of these factors when creating a seasonal temperature and precipitation outlook.
Short term weather features ultimately have the final say. Days or weeks of a stubborn area of high pressure can block Pacific storms from hitting California. A series of atmospheric river storms can turn an otherwise dry season into one with dangerous flooding.
Forecast models can’t highlight these kinds of details more than a couple of weeks out. Even then, California’s diverse geography and microclimates ensure that impacts will vary.
How should Northern Californians prepare?
El Niño does not guarantee a wet or damaging winter in Northern California, but it is a good reason to get ready for the wet season ahead of time.
That means the usual tasks like clearing gutters and drains at the end of the summer, checking the flood risk around your home, restocking emergency supplies, and making sure you can receive weather alerts quickly. Take a few minutes and sign up for your county or city’s emergency alert program.
For people in the Foothills, burn scar areas, or other flood-prone locations, it is also a good time to review evacuation plans before storm season ramps up.
The bigger picture is this: El Niño may raise the odds of certain impacts, but the actual risks to Northern California will depend on the day-to-day weather patterns that take shape later this fall and winter.
See more coverage of top California stories here | Subscribe to our morning newsletter | Find us on YouTube here and subscribe to our channel