Severe Thunderstorm Watch Issued Through 10 PM Monday

As of 5:50pm the risk for severe weather including damaging winds has increased. The development of numerous storms in a moist, unstable environment in the lee of the Appalachians have slowly clustered and grown upscale this afternoon. Within a modestly favorable low-level westerly shear environment (i.e., 0-3 km shear around 20-25 knots per mesoanalysis and local VWPs), continued upscale growth and organization is likely over the next few hours. As such, the threat for damaging winds will persist as multiple clusters progress eastward toward the higher terrain.

A Severe Thunderstorm Watch is in effect until 10:00 PM EDT this evening for a large portion of our region, including western North Carolina, eastern and Middle Tennessee, southeast Kentucky, southwest Virginia, far southern West Virginia, and portions of northern Georgia.

The primary concern with thunderstorms this afternoon and evening will be damaging straight-line winds, with scattered wind gusts potentially reaching 60–65 mph. While severe weather will not occur everywhere within the watch, the atmosphere is becoming increasingly supportive of storms capable of producing localized wind damage.

What We’re Watching

There are several ingredients coming together across the southern Appalachians this afternoon.

A remnant thunderstorm complex and associated mesoscale convective vortex (MCV) are helping provide additional lift and enhanced winds through the atmosphere. An MCV is essentially a small-scale area of rotation left behind by an earlier thunderstorm complex. These features can sometimes help organize or reinvigorate thunderstorms later in the day when they encounter a warm, unstable air mass.

That is what we are dealing with this afternoon.

The air mass across the region is very moist and increasingly unstable, and daytime heating will continue to help thunderstorms develop and strengthen. At the same time, our mountains will play a role. Terrain-driven circulations and differential heating along the higher elevations can provide additional areas of convergence and lift, giving storms more opportunities to develop.

With stronger winds also present aloft, thunderstorms that become well organized will have the ability to transport some of that momentum toward the surface.

Damaging Winds Are the Main Concern

The biggest threat through this evening is from thunderstorm downbursts.

A downburst occurs when a strong column of air accelerates downward through a thunderstorm and then spreads outward rapidly once it reaches the ground. In a very moist and unstable environment like this one, stronger storms can produce powerful downdrafts capable of bringing damaging wind gusts to the surface.

The Storm Prediction Center indicates that scattered damaging wind gusts up to around 65 mph are likely within the watch area.

Winds of that magnitude can bring down trees and large limbs, especially where soils are wet, and could result in scattered power outages. The wind threat may also be enhanced in some of the valleys and gaps where the terrain can locally influence wind direction and speed.

Small hail is possible in the strongest storms as well, but wind is clearly the primary severe-weather concern today.

Timing

We expect thunderstorm coverage and intensity to increase through the remainder of the afternoon.

The period we will be watching most closely is late afternoon through the early evening, when instability, moisture, terrain influences, and the approaching disturbance should overlap most favorably.

Storms will generally move toward the east-southeast at around 20 mph, although individual storm motions can vary.

Because storms may develop or strengthen fairly quickly, conditions can change considerably over a short distance. Some communities may see little more than rain and thunder, while locations underneath the strongest cells could experience damaging winds.

Watch vs. Warning

Remember that a Severe Thunderstorm Watch does not mean severe weather is occurring everywhere inside the shaded area.

It means the environment is favorable for severe thunderstorms to develop.

If a Severe Thunderstorm Warning is issued for your location, that means a storm capable of producing damaging winds and/or large hail is occurring or imminent, and you should move indoors and away from windows.

Although tornadoes are not the primary concern with this setup, severe thunderstorms can occasionally produce brief tornadoes. Any warning issued for your location should be taken seriously.

Keep phones charged, make sure you have a reliable way to receive warnings, and consider securing lightweight outdoor objects before storms arrive.

We’ll continue watching radar trends and how the atmosphere evolves through the afternoon and evening and will pass along updates as conditions change.