Very warm winter a gift from La Nina

Very warm winter a gift from La Nina
By RANDALL DICKERSON
NASHVILLE (AP) — From the Mississippi River to the Smoky Mountains, the winter just ended was warmer than usual all across Tennessee.
Forecasters use the me-teorological stretch of De-cember-February rather than the astronomical period between the winter solstice and the vernal equinox to denote the season.
It was the mildest winter in Nashville in 40 years, averaging 4.3 degrees above normal.
The National Weather Service reported the winter was 4.5 degrees above normal in Memphis. Knoxville and Chattanooga both ended the season at an average 4.4 degrees above normal while the Tri-Cities had a relatively balmy 4.6-degree deviation to the plus side.
In a sense, the unusually mild winter was something the wind blew in.
“When we have a La Nina situation like we did during the winter months, the main branch of the polar jet is well north of the Tennessee Valley,” said Bobby Boyd, a meteorologist with the National Weather Service office in Nashville. “The southern branch is moving across the Desert Southwest, the Southern Plains and the lower Mississippi Valley, bringing us warmer temperatures.”
La Nina and El Nino are the opposite phases of surface temperature variations in the Pacific Ocean.
In the La Nina, or cold phase, winter temperatures in the continental U.S. are warmer than normal in the Southeast and cooler than normal in the Northwest.
Another weather phenomenon also came into play.
“Arctic oscillation was in a positive phase,” Boyd said. “This year, most polar air spilled into Europe and Russia.”
There was officially only 0.4 inch of snow during the winter in Nashville. More fell in other places, including the northern Cumberland Plateau, the mountains and some in West Tennessee. Some school systems that had banked snow days used a few for health reasons instead; to break the cycle of local flu outbreaks.
Boyd said he went back over several decades of records, correlating temperature and snowfall, and wasn’t surprised to find the coldest winters are also the snowiest.
The visible results were dramatic: ornamental shrubs blossoming at Christmas, daffodils opening up in January.
The resulting early spring could translate into a stronger beginning to the travel season said Susan Whitaker, commissioner of the Tennessee Department of Tourist Development.
“People get out when the weather is nice,” she said.
So do the bugs.
Dr. Frank Hale, an entomologist with the University of Tennessee Extension, said the effects of frigid weather on the insect population are overrated.
“For the vast majority of insects, it doesn’t make much difference,” said Hale from his office at the Ellington Agricultural Center in Nashville. “Mosquitoes are just as bad or worse in Alaska than they are in Tennessee.”
The spring weather has more to do with the mosquito population, he said. Early warm weather with moist conditions allows them to reproduce earlier and more generations of them hatch out before frost comes again. The fertile little bloodsuckers can go through a generation in a month or less and Hale says each successive generation tends to be larger than the one preceding it.
Garden pests might be detected earlier in the season.
Hale recommends keeping the insect repellant handy because mosquitoes can carry west Nile disease and ticks can harbor Lyme disease and Rocky Mountain spotted fever.
Nothing in the current forecast would discourage enjoyment of the outdoors.
Expected high temperatures into the weekend will be within 5 degrees above or below 80 statewide.
Joe Edwards in Nashville contributed to this story.
Published in The Messenger 3.14.12

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