The atmosphere is being primed for thunderstorm development across the Cumberlands.
That is the situation as we hit mid-afternoon on the northern plateau. An atmospheric cap that has been in place, which helps inhibit thunderstorm development, is being eroded by broken cloud cover and diurnal heating. And outflow boundaries from thunderstorm activity to our west this morning have been laid down across the northern plateau region. Those two factors create a conduciveness for thunderstorms in an atmosphere that is moderately unstable with moderate wind shear, and forecast soundings continue to indicate the potential for large hail and high straight-line wind gusts wherever thunderstorms do develop.
As if on cue, the 3:15 p.m. radar update shows convection blossoming across Middle and West Tennessee, primarily along the I-40 corridor (and further north in central Kentucky). So far, none of the storms in Tennessee are strong enough to warrant severe thunderstorm warnings, but the situation continues to evolve. Of particular noteworthiness is a piece of upper level energy that is rotating through the region, which could help erode the atmospheric cap and help organized thunderstorms develop over the next couple of hours.
The Storm Prediction Center has issued a severe thunderstorm watch for parts of northern Middle Tennessee and southern Kentucky, including Fentress County, until 10 p.m. EDT. In the watch, the SPC mentions the potential for large hail up to 2.5 inches in diameter, along with damaging straight-line winds up to 80 mph. The tornado threat is very low.
The possibility remains that the severe thunderstorm watch box will expand eastward with time, particularly if conditions continue to become more favorable for storm development. For now, the National Weather Service at Morristown is forecasting a 60 percent chance of thunderstorms today, tonight and tomorrow. A broken line of thunderstorms is developing along a line from about Crossville to Lebanon and pushing northeast, and will eventually impact the northern plateau region.
The risk for severe weather should begin to diminish by sunset.
A second severe thunderstorm threat may evolve tomorrow morning, although meteorologists are uncertain about just how it will develop. Tomorrow's threat will be completely dependent upon how the weather scenario unfolds tonight.