And the previous record wasn’t even close.
The average amount of precipitation to fall across the Tennessee River Valley basin in 2018 was 67.1 inches, a full two inches more than the previous record of 65.1 inches set in 1973.
The Tennessee River Valley encompasses all of East Tennessee, much of Western North Carolina, parts of northern Alabama and even a section of southwest Kentucky.
“I think what’s interesting about breaking the rainfall record is that we didn’t break it gently,” James Everett, manager of the Tennessee Valley Authority’s River Forecast Center, said.
However, the annual precipitation record did not appear to be in jeopardy in early December, as weather forecasts predicted the year would conclude with average or below-average rainfall.
“The forecast actually looked kind of dry heading into the new year. (We) didn’t think we were even going to get close to breaking the record, and then it turns out, those last few weeks of December brought about 5 inches of rainfall across the valley,” Everett said.
“Certainly, the first half of December was a lot more towards the normal side, in terms of precipitation. (T)he signals heading towards mid-December that we were getting from the (National Weather Service) was normal precipitation to maybe a little bit below normal. Then, toward the end of last month, things really turned on, and we had multiple systems move through within days of each other, bring 2-to-3 inches (of rain) at a time.”
Everett said high rain totals, particularly in mountainous areas like Boone, North Carolina, helped pull the annual average up. A TVA rain gauge atop Mount Mitchell in North Carolina reported 118.8 inches of rainfall for the year.
Even areas in the valley, like Athens, Tennessee, reported more than 70 inches of rainfall, Everett said.
“It’s pretty common for us to get high rainfall totals in the mountains. It’s just wetter up in the mountains — not usually 90-to-120-inches wet — but down in the valley proper (in lower elevations), it’s really uncommon to get some of those 70-to-80 inch totals,” he said.
At Tri-Cities Airport, the National Weather Service in Morristown reported a total of 53.84 inches of rain in 2018, roughly 12.83 inches more than the average 41.01-inch total but considerably less than the 65.64-inch record set in 2003.
The wettest month for 2018 at the Tri-Cities Airport was May with 7.85 inches of rain, but still less than the 12.70 inch-record set in July 2012. Every month of 2018 surpassed its average precipitation rate except for January, April, June and July.
All this additional precipitation will certainly keep the Watauga, South Holston and Boone dams busy over the coming weeks and months, Everett said.
“We use those dams, we call them tributary storage reservoirs, to store water and help reduce flooding downstream,” he said.
“So we saw the lake level at Watauga rise to above-summer pool levels. We use operating guides as targets to maintain certain levels of flood-storage capacity, given the time of year. Normally, what we do during the fall is draw these reservoirs down, and that’s exactly what we did to create storage room for heavy rain events.”
Much of that storage space has been used to store December’s heavy rain totals so Everett said TVA will soon be releasing water downstream to prepare lake levels for more winter precipitation. He said 60 percent of the annual runoff typically occurs between January and March, a period often referred to as the “wet season.”
“It only takes a few days for us to rise lake levels by 10 or so feet, but it takes weeks to release that water in a controlled manner and bring the lake back down. So that’s what we’ll be doing over the coming weeks,” Everett said. “We’re going to be running a lot of these turbines that generate power around the clock or near-around-the-clock producing hydroelectricity.”
To maintain Boone Lake’s levels during construction, spokesman Travis Brickey said TVA will likely start using a sluice gate to pass some of the excess water through the dam, which could create a high-arching spray known as a “rooster tail.”
“A lot of people are not used to seeing that, but it’s perfectly normal,” Brickey said. “The abnormality of how much rainfall we’ve had, we just can’t hold onto it indefinitely. We do have to start releasing it through the system.”