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La Niña affects long-range forecasts
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La Niña affects long-range forecasts

Precipitation and temperature maps for May, June and July of 2021

Precipitation and temperature maps for May, June and July of 2021 show a La Niña pattern could make for active storm events this spring. Long-range forecasting uses these climate phenomenon combined with historical data and patterns to help create these outlooks.

Weather is one of the biggest variables to a farm operation. Knowing how many inches of rain will be coming, even a few days out, can be a challenge. When it comes to predicting what will happen in the 2021 season, that’s an even bigger undertaking.

For meteorologists making those long-term outlooks, methods of forecasting are seeing advances which make for more accurate predictions. One of those tools is looking outside the Midwest and toward the coasts.

“One of the things that has come to light, for me, is the significance of ocean temperatures,” eastern Iowa meteorologist Terry Swails said. “They play a huge role in climate and long-range forecasting. That’s something I’ve started to pay a tremendous amount of attention to.”

Jon Gottschalck, with the Chief Operational Prediction Branch at the National Oceanic Atmospheric Association (NOAA), said there are three main areas the weather service looks at when developing long-range forecasts. The first is ocean temperatures and oscillations such as El Niño or La Niña.

“That’s by far the biggest seasonal predictor from a purely phenomenon point of view,” Gottschalck said. “Depending on the phase, we know there’s certain temperature and precipitation patterns that are more or less reliable.”

Another weather phenomenon called the Madden-Julian Oscillation measures convection over the tropical Pacific Ocean and Indian Ocean. Swails said there are eight phases in which the oscillation can develop, allowing forecasters to form an outlook based off those trends.

La Niña is “pretty strong” right now, Gottschalck said, which means cooling on the equatorial Pacific Ocean. For the continental U.S., that will change the Jetstream, bringing possible storms and making for a cooler winter.

Gottschalck said the second area NOAA watches are observational variables and how they relate to historic weather patterns. These could include sea level surface pressure or wind speeds in different parts of the atmosphere.

“We have historical data going back 50-100 years depending on the data sets,” he said. “When we have certain patterns we can get statistically significant predictors for temperature and precipitation based on real, physical relationships.”

The third tool in the forecasting toolbox is using forecast models. Gottschalck said these aren’t models that look 100 years out for climate change-related purposes, but are short-term models that help create daily forecasts.

“They are just extended out several months, in many cases to five or six months, and they rely more on what we call conditions that have climate memory,” Gottschalck said.

Referencing the Midwest, he said a large part of this is utilizing soil moisture and snow conditions, which will have a heavy effect on the weather to come.

Gottschalck stressed that when looking at the long-term forecasts, the accuracy will tend to be better in the early portion of the outlooks compared to several months or a year out. The further out a prediction goes, the more variability that comes in to play.

“It depends on some of the factors that are at play,” Gottschalck said. “Right now we have a pretty strong La Niña so confidence and reliability in our outlooks should increase. This winter, for example, our confidence is higher than if we had neutral conditions.”

Swails said one of the improvements, or advancements, he would like to see made in long-range forecasting is finding more ways to measure the ocean temperature and recognizing changes that take place sooner.

“Seventy percent of Earth is water,” Swails said. “There’s a whole lot of that out there. When you look at the world climate, understanding that area better and getting quicker, more accurate data from these vast regions of water is going to improve that modeling.”

Adding to the challenge of long-range forecasting is the looming threat of climate change, Swails said. Going back 30 years, he noted there might be only a 2-3 degree difference in average temperatures. While that may seem like a small number, Swails said it has drastic effects.

“It can make a huge difference in terms of how much snow (we receive),” he said. “If you don’t have the snow on the ground, that’s going to mean warmer temperatures and a lot of other variances that come with that. It’s also going to mean more water vapor, which may tend to limit temperature extremes. It compressed our temperatures into a narrower range, but we have higher dew points which makes for steamy conditions.”

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