Not All El Niños Are Created Equally

As winter approaches, more and more people are becoming aware of El Niño. Did you already know about it? If so, great. If not, you have time to learn and prepare. It is a significant factor in weather forecasts for the next 6 months. Meteorologists in many areas of the country, and the world, will be busier than normal. In other words, it is likely to impact you directly or indirectly.

As you might expect, media sources are using it to drive a little hype and interest. Well, actually, more like full-blown climb the tallest tower and scream HYPERBOLE! Here is how the L.A. Times wants to grab your attention:

The El Nino Godzilla Fights the Blob and all of California is to Perish, or maybe not.

Maybe cartoons are a better attention grabber than the written word. However, this isn’t an article critiquing cool cartoons of fictional radioactive lizards and blob metaphors. This is an article about the current El Niño status and how each El Niño is different.

As of September 28th, 2015, El Nino conditions in the equatorial Pacific are quite strong. Sea surface temperatures are above average by an order of 2 degrees Celsius. This small number is an enormous increase in potential energy, higher than average, residing in the pacific waters. Some of this energy disperses through hurricanes in the higher than average eastern and central pacific hurricane season. However, during the winter, December through March, the excess energy disperses by a stronger subtropical jet stream coming out of the Pacific and crossing the southern United States. This plays out in more rainy and stormy weather and sometimes that creates significant problems. So, does a stronger El Niño mean more energy impacts the United States, and is it directly proportional? First, here is the current status across four regions of the Pacific (SST is sea surface temperature):

Four El Nino Regions of Tropical Pacific

El Niño 3.4 is the standard for comparing El Niños. As you may have guessed it blends region three, central pacific, with four, the more western El Niño region of the pacific. Region 3.4 is 2.3 degrees Celsius above normal. There are only two El Niños since 1950 that compare with this warm anomaly – 1982/1983 and 1997/1998. In fact, El Niño 2015/2016 may end up being the warmest on record. Since 1950, there have been twelve El Niños during the winter months and we are now entering our thirteenth. Three month historical strength, of El Niño, are found at the Oceanic Niño Index (ONI). Records go back to 1950.

In review of earlier El Niño winters, I divided ONI into weak (.5 to 1.0), moderate (1.1 to 1.5) and strong (>1.5) using the three-month ONI. The weak El Niños were 1953, 1969, 1995 and 2005. The moderate El Niños were 1958, 1966, 1973, 1987, 1992 and 2010. The strong El Niños were 1983 and 1998. The generic forecast for an El Niño winter is wetter and cooler than normal across the southern United States with drier and warmer than normal conditions across the northern United States. Here is the current forecast for January through March 2016:

Temperature Forecast for Jan, Feb and March 2016

Precipitation Forecast for Jan, Feb and March 2016

For the three-month period, below average temperatures are found from New Mexico east to North Carolina and Virginia with above average temperatures for most of the northern United States. Above average precipitation is forecast from California east to the Atlantic coast with below average precipitation in the pacific northwest and the central United States along and east of the Mississippi River.

Now I want to use historical data (December through March) from the previous El Niños and see how they compare to normal temperatures and precipitation. Let’s start with the weak El Niños of 1953, 1969, 1995 and 2005.

US Temperature Anomalies in Weak El Ninos

US Precipitation Anomalies in Weak El Nino

In weak El Niños, historical records (December through March) show that most of the United States experiences above average temperatures with normal precipitation. A large area of the United States experiences temperatures 2 to 4 degrees Fahrenheit above average. The one area with a significant spike in precipitation is California – 6 to 10 inches above average. New England has slightly above average precipitation and the southeast United States shows some areas of less than average precipitation. So a big heat signature and isolated areas of precipitation anomalies.

So how does it look for a moderate El Niño? Well, here are the temperature and precipitation anomalies for 1958, 1966, 1973, 1987, 1992 and 2010, a slightly larger sample size.

The temperature profile changes much compared to a weak El Niño. The northern half of the United States still shows a warmer than average profile with highest anomalies, near 5 degrees, in the Dakotas and Minnesota. The southern half of the United States experiences below average temperatures from California to North Carolina. The largest anomalies are in Texas and Louisiana with temperatures around 3 degrees below average. The national temperatures looks like a ying and yang profile. For precipitation, below average precipitation falls in the pacific northwest and around Kentucky. Western Washington and Oregon see rainfall deficits of 6 to 8 inches with 2 to 4 inch deficits in Kentucky. Normal to slightly above normal precipitation falls in California and Arizona. A larger area of increased precipitation develops from Texas east to South Carolina, Georgia and Florida. Where rainfall amounts increase by 2 to 6 inches above average.

So, how does a strong El Niño show up in historical anomalies for temperature and precipitation? It is a small sample size, but it is all we have on record. 1983 and 1998 were the two strongest El Niños on record and align, in magnitude, with our current El Niño.

US Temperature Anomalies in Strong El Ninos

Strong El Nino Precipitation Anomalies

The strong warm temperature bias continues across the northern United States with peak anomalies around 6 degrees in North Dakota, Minnesota and northern Wisconsin. The southern half of the United States experiences near normal temperatures. Precipitation is above normal, much in California, for the west coast and Arizona. Rainfall of 3 to 20 inches above normal fall in these areas. That is huge! A large area of above normal precipitation falls from Texas and the central plains east to the Atlantic Ocean. Most of this area sees an increase of 3 to 9 inches of rain. Kentucky, just like in a weak and moderate El Niño, is an isolated area of below average precipitation with rainfall deficits of 3 to 4 inches.

So, what is the take away? Actually, there are quiet a few. For one, the northern United States experiences above average temperatures in every El Niño – weak, moderate, or strong. Below average temperatures are only experienced in the south during moderate El Niños. Weak El Niños bring more rain and snow to California than moderate, but not as much as strong. Strong El Niños see the greatest increase in precipitation for California and most southern states. Moderate to strong El Niños also produce an increase in precipitation up the east coast into New England. Another interesting note is that the current United States temperature forecast for this winter resembles a moderate El Niño and the current precipitation forecast mirrors a strong El Niño. What gives?

Well, for one, we are talking about a small statistical sample. Sixty five years of data is great but six hundred and fifty would be better. Unfortunately, that data does not exist. So, the mapped data above is not a guarantee this winter. It is guidance. Secondly, there are other factors in the current forecast. El Niño isn’t the only oscillation with impact this winter. It is a strong one, but not a stand alone. In the Great Lakes and New England, the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) could have an impact on temperatures and precipitation. These are smaller scale oscillations with a time period of a week to a month. So, unlike El Niño, you cannot project a positive or negative AO, accurately, for winter 2015/ 2016, six months in advance. On that shorter lead time, they can bring very cold air into the eastern United States and aid in developing strong storms along the east coast. We will have to wait until December and January to see how the AO and NAO develop.

This is the 30,000 foot view of the upcoming El Niño Winter 2015/2016. I can tell you that when research of earlier El Niños goes down to state or city level, the frequency, intensity and type of weather events are found. And that data is used to find a more accurate assessment of what is expected this winter. Be aware and resilient my friends. If you have questions about this article or the upcoming El Niño, feel free to email me. In the meantime, enjoy watching Godzilla through Redbox or Netflix during the stormy weather this winter.