El Nino Promises Unusual Tennessee Winter (380)

KNOXVILLE, Tenn.– Tennesseans will likely feel El Nino’s effects this winter, but it’s too soon to predict temperatures and precipitation, a University of Tennessee climatologist said Tuesday.

 “The message right now is be prepared for a much more unusual winter than we have seen recently,” said Dr. Ken Orvis, an assistant professor in the UT-Knoxville Department of Geography.

 El Nino is a world-wide weather maker created every few years by Pacific air and ocean currents. This year’s El Nino is the largest and most powerful since records have been kept.

Prevailing winds usually flow east to west from the coast of South America toward Australia and Indonesia. In El Nino years, the winds die down, causing water temperatures in the Eastern Pacific to rise as much as 10 degrees.

Tennessee’s weather this winter depends on how El Nino conditions develop off the coast of California and how those conditions influence the flow of a high altitude air current called the jet stream.

 “It could be a colder winter, but it depends on how the jet stream sets up,” said Orvis, who wants to see how far north over the Rocky Mountains the airflow establishes itself.

Even in years when there is no El Nino, forecasting winter weather in Tennessee is no easy task.

 “We have warm air coming up out of the Gulf of Mexico and the continental air from the north and we are in between,” Orvis said. “One hundred miles to the north or 100 miles to the south, the weather is easier to predict.”

 To further complicate predictions, the Atlantic Ocean has its own oscillation, which last year switched to a cold phase for the first time in 20 years, Orvis said.

 “That can change the way the jet stream flows over the United States,” Orvis said.

 So far this El Nino’s influence over Tennessee’s weather has been negligible.

 “What we get is much wetter than usual air in the high altitude of the upper troposphere,” Orvis said. “If thunderstorms are developing, those get much bigger, much faster and more rain falls from them than usual.”

 Absent thunderstorms, Tennessee’s usual rain maker during the summer and early fall, the moist Pacific air passes over the state with no precipitation, Orvis said.

 The first sign of this year’s El Nino became evident over Tennessee during February in the form of a high altitude Pacific airflow, which may have contributed to Tennessee’s cool, wet spring. Orvis said.

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 Contact: Dr. Ken Orvis (423-974-2418)