El Nino Warning sign MCCAIG/Getty Images
WEATHER AHEAD: Looks like ocean waters in the Pacific could be warming, which could bring a change to Western weather. Often, drought is the key impact for El Niño.

A change in the weather

Precipitation patterns may change with the El Niño predicted for the coming winter.

Weather and climate patterns can be the most beneficial, and detrimental, to agriculture. The National Oceanic and Atmospheric Administration tracks these patterns, and recently released an El Niño watch — with a 70% probability — for the 2018-19 Northern Hemisphere winter. To predict an El Niño, NOAA’s National Weather Service Climate Prediction Center forecasts tropical Pacific Ocean temperatures.

“Measurements are taken by ocean buoys and satellites,” explains Michelle L’Heureux, a meteorologist with the Climate Prediction Center, “as well as ships that travel through that area recording water temperatures. When we declare El Niño, that means temperatures in the Niño 3.4 region rose at least a half-degree Centigrade above average, and this is forecasted to persist for at least six months.”

El Niño effects
El Niño prediction models are based on both surface and deep-water ocean temperatures. Warm ocean temperatures affect rainfall and wind patterns, which shifts the jet stream of strong, predominantly westerly air currents encircling the globe several miles above the Earth. Another indicator is that trade winds weaken from east to west over the equatorial Pacific Ocean.

“What happens in the tropical Pacific doesn’t stay in the tropical Pacific,” said L’Heureux. “This is because it’s such a huge ocean basin that contains tremendous heat and energy. When the climate shifts in the tropics and the heating source moves, the jet stream over the northern Pacific Ocean will often move south. This shifts the flow of air and moisture from the northern United States to the south.”

The last significant El Niño took place in the winter of 2015-16 and was one of the strongest recorded in the past 60 years. This particular El Niño caused above-average rainfall in the Northwest U.S., which contradicts the historical record of below-average precipitation.

“We are very realistic that there are climate elements that we can’t forecast,” L’Heureux says. “But you will come out ahead over many years, because the forecast is based on probability. Ultimately, over time, more forecasts will be accurate than not.”

Temperature and precipitation climate outlooks over the U.S. are issued for three-month averages. L’Heureux says that the climate forecast for October through December 2018 for the Northwest U.S. favors below-average precipitation, in part because of the impending El Niño.

Tracking weather trends
The NWS Climate Prediction Center publishes an ENSO (El Nino Southern Oscillation) update on the second Thursday of every month. 

You can also track climate forecasts at the ENSO blog of climate.gov.

Find seasonal forecasts at the NOAA Climate Prediction Center webpage.

El Niño vs. La Niña
El Niño is the warming of the tropical Pacific Ocean, and La Niña is when temperatures cool. The term ENSO (El Niño Southern Oscillation) encapsulates both La Niña and El Niño — and even the neutral, normal position of climate.

Hemken writes from Lander, Wyo.

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