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Updated from the Field: Who Ordered La Niña for Taco Tuesday?

Posted by Dave Dyson, Agronomist on September 24, 2020

While drinking coffee at the local watering hole these past few weeks, I have been hearing a lot of grumbling about the “crazy” weather we have been experiencing this fall. According to NOAA, the weather pattern we are in right now is not new or unexpected. Weather groupies, like myself, have been looking forward to this phenomenon all year. The weather pattern that we are entering right now is called La Niña.  

There are two major weather occurrences that are centered across the central and east-central equatorial Pacific (between approximately the date line and 120⁰W). The first is called El Niño, which refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea-surface temperatures. El Niño represents the warm phase and is sometimes referred to as a Pacific warm episode. El Niño originally referred to an annual warming of sea-surface temperatures along the west coast of tropical South America. The second meteorological event is called La Niña which refers to the periodic cooling of ocean surface temperatures in the central and east-central equatorial Pacific that occurs every three to five years or so. La Niña represents the cool phase and is sometimes referred to as a Pacific cold episode. La Niña originally referred to an annual cooling of ocean waters off the west coast of Peru and Ecuador. 

During an El Niño or La Niña, the changes in Pacific Ocean temperatures affect the patterns of tropical rainfall from Indonesia to the west coast of South America, a distance covering approximately halfway around the world. These changes in tropical rainfall affect weather patterns throughout the world, Figure 1. The fluctuations in ocean temperatures during El Niño and La Niña are accompanied by even larger-scale fluctuations in air pressure between the western and eastern tropical Pacific known as the Southern Oscillation. During El Niño, higher than average air pressure covers Indonesia and the western tropical Pacific, and below-average air pressure covers the eastern tropical Pacific. These pressure departures are reversed during La Niña, which features below-average air pressure over Indonesia and the western tropical Pacific and above-average air pressure over the eastern tropical Pacific. 

Figure 1: Forecasted La Niña weather map

So, if we are entering a La Niña event in the central Pacific Ocean, what does all this mean for our U.S. weather pattern in the winter of 2020 and spring of 2021? A typical La Niña winter in the U.S. brings cold and snow to the Northwest and unusually dry conditions to most of the southern tier of the U.S., according to NOAA’s prediction center. The Midwest will most likely see warmer temperatures and wetter conditions, and the Southeast to the Mid-Atlantic States will also tend to see warmer-than-average temperatures during a La Niña winter., Figure 2.  

Figure 2: This diagram shows the breakdown by month for an expected El Niño or La Niña.


  • El Niño means warmer Pacific water 
  • La Niña means cooler Pacific water 
  • We are entering a La Niña weather pattern 
  • The Midwest will most likely see wetter and warmer conditions 



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David Dyson

Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at

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