Midwesterners hoping for a calm stretch of weather after a cold, snowy winter might be disappointed.
Tony Lupo, department chair and professor of atmospheric sciences in the College of Agriculture, Food and Natural Resources at the University of Missouri, says the approaching spring could be stormier than normal.
However, Lupo forecasts a relatively calm year for Tornado Alley, which cuts through Texas, Oklahoma and Kansas. Atmospheric models predict a dryer than normal spring and summer, taking away the fuel for super-cell storms, which often spawn tornadoes.
La Niña, the atmospheric phenomenon that spawned winter blizzards through much of the country, generally shifts spring and summer thunderstorm activity northward. Lupo thinks La Niña will lead to increased spring and summer thunderstorm activity in states north of Tornado Alley, including Nebraska, Iowa, northern Illinois and Indiana.
La Niña occurs when cooler than normal water temperatures develop in the Equatorial Pacific Ocean. The impact is most clearly seen in wintertime, when it can bring cold weather extremes to parts of the nation.
In a La Niña season, the jet streams pick up warm Pacific moisture and direct their cargoes of warm and unstable air to Nebraska, Iowa, Illinois and Indiana. Storm systems tend to follow these streams.
“There has to be heat and moisture to build severe thunderstorms,” Lupo says. “An atmosphere that is too cold or dry will not produce dynamic cloud systems like super-cell storms. When the jet stream is farther north, as it is in a La Niña event, you have a better chance of achieving these kinds of temperatures and dew points in these parts of the country.”
La Niña’s opposite, El Niño, is associated with warmer water temperatures. In the continental U.S. during El Niño years, temperatures in the winter are generally warmer over the north, Midwest and east.
In a typical El Niño or neutral year, the jet stream travels farther south through Texas, Oklahoma and Kansas – Tornado Alley.
“There is no statistical data that storm intensity or duration differs between La Niña and El Niño years nationwide,” Lupo said. “However, our data from the 1950s and 1960s relied on human observation which can be spotty and inaccurate. We only have a few years of reliable national Doppler radar and satellite imagery.”
Lupo is a member of the Global Climate Change Group, which researches planetary-scale atmospheric processes, specifically a phenomenon called atmospheric blocking. One of the rarest weather events, blocking can trigger dangerous conditions such as a 2003 European heat wave that caused 40,000 deaths. Blocking usually results when a powerful, high-pressure area gets stuck in one place and, because they cover a large area, fronts behind them are blocked.
“In this research, we’re trying to see if increased carbon dioxide in the atmosphere and the resulting atmospheric warming will affect the onset and duration of future blocking events,” Lupo said. “We’re hoping that the research will add cues that could help fellow forecasters better predict blocking and warn people in cases of long-lasting, severe weather.”