Would it surprise you to know that much of Tennessee is in the early stages of drought?
It’s true. The U.S. Drought Monitor — a collaborative effort of several federal agencies, such as the National Weather Service and U.S. Dept. of Agriculture — classifies roughly 55% of Tennessee — including Scott County and the northern Cumberland Plateau region — as being “Abnormally Dry,” which is one step below an official drought.
Now, there are a couple of caveats that deserve to be mentioned with that, including the fact that the current classification is based on data through Feb. 23. The Drought Monitor will be updated on Thursday with data that is current through today. And, given the several inches of soaking rains that we saw over the weekend, it’s possible — if not likely — that we’ll see the “Abnormally Dry” areas scaled back somewhat when the update is released.
But 2021 has certainly started quite different from the past few years. We saw a lot of snow and wintry weather in January and February — 9 inches of snowfall were recorded in Oneida in February, and most of Scott County saw more than that — and cold weather is usually not wet weather.
January featured below-normal rainfall in Oneida: 2.6 inches, compared to the norm of 4.5 inches. February’s rainfall was above-normal, 4.6 inches compared to the norm of 4.0 inches, but most of that rain fell in the final few days of the month — after the last Drought Monitor update.
The rain we saw to end last week, and through the weekend, pushed us to normal for the year-to-date, at 8.8 inches since Jan. 1. But it’s still quite different from the past three years, each of which featured more than 10 inches of rainfall in the month of February alone.
And even if the next Drought Monitor update removes us from the “Abnormally Dry” category, where are we headed as we progress into spring and then summer?
Currently, drought is raging in the western U.S. Nearly the entire western half of the country is in varying stages of drought, with much of the Desert Southwest and the southern Rockies being in a severe drought. Meanwhile, most of the eastern U.S. is drought-free at the moment. That’s typically the way it happens — if one side of the country is seeing plenty of rain, the other side isn’t seeing enough rain. And, for now at least, the NWS’s Climate Prediction Center isn’t forecasting a change in the haves and have-nots when it comes to America’s water supply — at least not through the month of March.
But seasonal drought is about more than a single month, and there are reasons to think we could be headed into a summer drought.
First, though, the near term: With light rain moving out of the region tonight, there are some models that aren’t showing a single drop of rainfall for the next week. The official forecast from the NWS is for a string of sunny — though cool, for the most part — days through the early part of next week.
With that in mind, we could be headed for below-average rainfall again in March. It’s typically the third-wettest month of the year in Oneida, just behind May and December, and featuring just a little over five inches of rain.
There are strong storm signals showing up for the middle of the month; we could end up with a couple of different storm systems that dump quite a bit of rain. But will it be enough to finish the usual late-winter filling of our reservoirs before we move into the drier months of late spring? The persistent ridge of high pressure in the Atlantic Ocean that prevented us from seeing even more snow and cold than we did in February is going to flex its muscles at times over the next month or so, which should help shove the storm track further north, leaving at least parts of the Southeast with below-average rainfall for this time of year as we move through late March and into the middle of April.
At the same time, the broader atmospheric pattern that we’re in is one that suggests above-average rainfall for much of the Midwest, and if the southeast ridge gets beat back enough by persistent storms, we could see ample rainfall extend further south, into Tennessee and the rest of the Mid-South. The CPC’s long-range forecasts indicate that possibility, keeping below-average rainfall centered over the southwestern U.S. for the month of March and the three-month period of March-May, while in the eastern U.S. the below-average rainfall is relegated primarily to the Gulf Coast and Florida.
Even if we make it through spring with sufficient rainfall, we could find ourselves dealing with drier conditions further into summer.
One thing to watch right now is the state of the ENSO, or water temperatures in the Pacific. We’re in a La Nina phase, which typically means a weaker-than-usual subtropical jet stream, increasing the risk of prolonged dry periods in the Southeast. Will La Nina fade with the arrival of warmer weather in the U.S., or will it persist?
The last time we saw a multi-year La Nina was 2010-2012, and 2012 just also happens to be the last very hot and dry summer that we saw in this part of the world. That year, we saw ample rainfall through the winter and spring. But as June began, things began to dry out across much of Tennessee. We finished the year with just 45 inches of rain, about 9 inches below normal. The temperature for the year was three degrees above normal in Oneida.
So far, most experts aren’t ready to suggest that 2021 could be a repeat of 2012 in terms of drought, but there is plenty of reason to think we could be somewhat warmer and somewhat drier than normal as we move from spring to summer, and at least periods of drought are possible, especially if La Nina conditions persist.