La Niña could make spring a bumpy ride

April 11, 2006

The current La Niña-controlled weather patterns have the potential to produce additional severe weather like what has hit Indiana, the Midwest and the South during the past couple of weeks, said state climatologist Dev Niyogi.

Based on historical data, Indiana's spring is expected to be wetter than normal with extreme variations in temperature, but La Niña makes predictions difficult, said Niyogi, who also is an assistant professor of agronomy and earth and atmospheric sciences at Purdue University. The official National Oceanic and Atmospheric Administration spring forecast is for an equal chance of precipitation and for temperatures to be above or below normal.

La Niña's continued influence is expected to persist for several months into late spring, Niyogi said. If the wet spring foreshadowed by historical data occurs, it also could impact crop planting.

"La Niña weakening should lead to a somewhat average spring season, both in terms of temperature and precipitation," Niyogi said. "However, that is deceptive because historically La Niña usually leads to wide swings in weather conditions.

"So, even if the average conditions would be somewhat normal, a La Niña spring is notorious for a rollercoaster weather pattern. Some days people will ask, 'Is the summer already here?' Some days they'll say, 'It looks like we never left winter.'"

La Niña occurs in a natural cycle about every two to seven years when ocean waters in the Pacific equatorial region are cooler than normal, Niyogi said. The phenomenon is caused by the circulation and interaction of cold and warm ocean water.

"We are still trying to understand the factors that contribute to La Niña and El Niño driven weather pattern changes," Niyogi said. "Observations tell us whether the oceans are warmer or cooler, and then we respond to what might be happening in the months after that."

This weather variability depends on the persistence of La Niña, he said. Already this year, spring weather has been marked by severe storms and tornadoes in the Midwest and the South.

The good side of these storms is that it usually means enough rain occurs to overcome drought conditions, Niyogi said. The negative side is the potential for tornadoes, lightning and flash floods.

Forecasters will be closely monitoring precipitation over the next couple of weeks to determine if northern Indiana, hit with severe drought last year, is receiving enough rain to rebound to normal soil moisture levels. Indianapolis was dry over the winter, with 75 percent of the normal amount of snowfall, but in March, rainfall measured more than 3 inches above normal.

Overcoming the precipitation deficit is important to farmers, as is the timing of rainfall, said Kenneth Scheeringa, associate state climatologist.

Looking at the La Niña -driven weather events over the past 14 years and also at overall climate events, it's likely that May will be much wetter than average, he said.

"Generally, La Niña begins in mid- to late-spring or in the fall; this year it began in January," Scheeringa said. "Looking at past La Niña events, when they started early, May was very wet in Indiana."

Weather experts remind people to use precautions in the event of severe weather, including thunderstorms, high winds and tornadoes. Severe weather tips include:

• Finding shelter inside.

• Going to an interior room on the lowest level of the building.

• Staying away from windows.

• Not standing under trees.

• Unplugging appliances.

• Having a flashlight, battery-powered radio, weather radio, bottled water and some canned food in your emergency area.

Source: Purdue University, by Susan A. Steeves