El Nino Returns, Could Upset Nation's Weather

Ken Scheeringa, acting state climatologist for Indiana, stationed at Purdue University, says that the last major El Nino 15 years ago caused memorable changes in our weather.

Early predictions by the National Weather Service say that this El Nino is even more severe than the 1982-83 episode.

"It appears that El Nino is roaring back, and this one is showing signs it could become more intense than the one in 1982-83," he says. "That year parts of the central United States had a Christmas day in the 60-degree range."

The effects of El Nino are always the most apparent near Christmas, and the name "El Nino" refers to the Christ child.

"What we're in now is the opposite of an El Nino," Scheeringa says. "In the Midwest we're feeling the influences of a weather pattern known as 'La Nina.' With this the ocean surface temperatures are cold, and since the end of last year and the beginning of this year we have been in a predominately cool weather pattern. That's why parts of the country have seen such cool temperatures this past winter and into the spring. That appears to be changing, perhaps in a very intense way."

According to Scheeringa, the El Nino weather pattern could bring unusually warm and dry weather to the Midwest, especially in the winter months.

El Nino weather patterns occur every few years, most recently during the winters of 1994-95 and 1987-88. The last major El Nino occurred during the winter of 1982-83. That winter, storms caused damage in California and the Gulf States resulting in an estimated 100 deaths and more than $2 billion damage.

Dayton Vincent, professor of atmospheric sciences at Purdue, says there is some disagreement among researchers about what causes El Nino, but there some characteristics that all weather scientists agree on.

Vincent says two events happen nearly simultaneously to create the weather pattern known as El Nino. "Water over the eastern Pacific, especially just south of the equator, becomes much warmer than normal during December and January," he says. "The second occurrence is that low-level winds from the region stretching from the western Pacific to east of the International Dateline become more westerly or, at least, less easterly than normal. This actually causes upwelling in the ocean circulation, and warmer waters come to the surface over the central Pacific to join those already over the eastern Pacific."

According to Vincent, wind changes in the lower atmosphere and in the Pacific Ocean cause a change in upper atmospheric circulation patterns. It's this upper atmospheric weather pattern, near jet stream levels, that ultimately influences weather in the United States, he says.

"It's well established that the southeastern part of the United States will see more cyclonic activity, and the northern Great Plains and south-central Canada will have more high pressure, so there are fewer storms and less rainfall," Vincent says. "In the Midwest, we lie in a zone that makes it difficult to tell if El Nino affects our weather. This spring we've had a lot of storms to the south while northern Minnesota and northern Michigan had better than normal weather. This could well be associated with the beginning El Nino conditions."

CONTACTS: Scheeringa, (765) 494-8105; e-mail, kenneth.l.scheeringa.1@purdue.edu; Vincent, (765) 494-3290; e-mail, dvincent@meteor.atms.purdue.edu

Compiled by Chris Sigurdson, (765) 494-8415; home (765) 497- 2433; e-mail, sig@ecn.purdue.edu