What is La Niña and What Does it Mean for West Texas?

Looking west from Lubbock, the smoke from the New Mexico fire creates an red-orange sunset (photo by Todd Lindley)
A red-orange sunset viewed from Lubbock on 12 March 2006. The color of the sunset was enhanced by smoke from wildfires burning in eastern New Mexico on that day. Photo taken by Todd Lindley.

What is La Niña?

La Niña is defined as cooler than normal sea-surface temperatures in the central and eastern tropical Pacific Ocean, as is depicted in the below graphic.  La Niña is important to weather forecasters because it impacts global weather patterns and can provide a clue regarding how the overall winter may unfold locally. La Niña conditions recur every few years and can persist for as long as two years, similar to El Niño.  Influences to the weather from La Niña and El Niño tend to be strongest during the winter season.

 

Average sea surface temperature (SST) anomalies (°C) for the week centered on 29 September 2010. Anomalies are computed with respect to the 1971-2000 base period weekly means. Image courtesy of the Climate Prediction Center.

Average sea surface temperature (SST) anomalies (°C) for the week centered on 29 September 2010. Anomalies are computed with respect to the 1971-2000 base period weekly means. Image courtesy of the Climate Prediction Center. 

 

To learn more about La Niña CLICK HERE.

 

To view common wintertime El Niño and La Niña influences across the entire United States CLICK HERE.

 

 

What Does the Development of La Niña Mean for the Weather Locally this Winter?

La Niña conditions have developed across the Pacific and they are expected to last at least into spring, with many of the forecast models predicting a strong episode (defined by a 3-month average Niño-3.4 index of -1.5°C or colder) from November through January before weakening (see the below plot for details).  Since La Niña conditions do influence large scale weather patterns, you may wonder what that means for the upcoming weather this winter across the South Plains region?

 

Forecasts of sea surface temperature (SST) anomalies for the Niño 3.4 region (5°N-5°S, 120°W-170°W). Figure courtesy of the International Research Institute (IRI) for Climate and Society. Updated 14 September 2010. The smaller the values on the graph (negative and below -0.5), the stronger the La Niña episode. Click on the image for a larger view.

Forecasts of sea surface temperature (SST) anomalies for the Niño 3.4 region (5°N-5°S, 120°W-170°W). Figure courtesy of the International Research Institute (IRI) for Climate and Society. Updated 14 September 2010. The smaller the values on the graph (negative and below -0.5), the stronger the La Niña episode. Click on the image for a larger view. 

Although exact conclusions are always tricky, as is the case with large-scale weather patterns and long range forecasts, there are some trends that can be noted across the South Plains that are correlated with La Niña. In general, La Niña episodes favor below normal precipitation and above normal temperatures for the region. Below are some observations made from previous La Niña episodes as compiled by Lubbock Warning Coordination Meteorologist (WCM) Jody James. The information is broken down by the strength of the La Niña episode as defined in the table below. The Oceanic Niño Index (ONI) is defined as the 3-month running mean of sea surface temperature (SST) anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW).  


La Niña Definition 

Oceanic Niño Index (ONI)

Weak

-0.5 to -0.9

Moderate

-1.0 to -1.4

Strong

-1.5 to -1.9

Extreme

-2.0 or less

The below information was compiled by examining precipitation information collected at the Lubbock airport. 


 Winter Precipitation (December through February)

Average Precipitation 1.88 inches normal
All La Niña Winters 1.56 inches 17% decrease
Strong to Extreme La Niña Winters 1.29 inches 31% decrease

Since 1950 there have been 13 La Niña episodes, including 6 strong to extreme episodes.  The above precipitation data is for climatological winter (December through February), while the snowfall data represents the cool season period from October through April. 

 Winter Snowfall (October through April) 

Average Snowfall 10.4 inches normal
All La Niña Winters 5.8 inches 44% decrease
Strong to Extreme La Niña Winters 5.2 inches 50% decrease


From the above tables we can see that:

  •  La Niña events favor a decrease in total precipitation at Lubbock, with strong to extreme episodes having a stronger signal.
  • There is a strong signal for a significant decrease in snowfall during La Niña episodes.

What does this all mean?

According to the current computer model forecasts it appears the ongoing La Niña episode will persist through this upcoming winter. Thus, there will be a greater than average chance that the South Plains region is drier and less snowy than normal this winter.  The official long range forecast for the United States reflects this, and can be found at the Climate Prediction Center by CLICKING HERE.

The development of La Niña is also well correlated with warmer than normal conditions across the southern United States during the winter.  The current long range forecast from the Climate Prediction Center for the South Plains calls for a high likelihood (50 percent or greater) of winter temperatures being above average.


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