Much-Needed Rain Comes With a Catch: Flash Flood Risk Through Friday

For months over the Spring and early Summer, we’ve been talking about the growing drought across western North Carolina and how badly we needed a widespread soaking rain. Well, it’s finally on the way—but it’s arriving with a downside. Over the last week and a half most of the area has received rainfall of at least one inch, some more. Now, over the next 36 hours, several rounds of heavy showers and thunderstorms are expected to move across the region. While this rainfall will certainly help chip away at the drought, some locations may receive too much rain too quickly, increasing the risk for flash flooding through at least Friday.

A slow-moving cold front is the driving force behind this active weather pattern. Instead of sweeping through the Carolinas, the front is expected to slow to a crawl and nearly stall over the region. That may not sound significant, but it creates an ideal setup for thunderstorms to repeatedly develop and move over the same communities.

We call this “training,” where storms follow one another along the same path much like train cars on a railroad track. Instead of one thunderstorm producing a quick downpour before moving away, multiple storms could impact the same area for several hours. That’s when flash flooding becomes a concern.

The atmosphere will also be loaded with tropical moisture. With exceptionally high moisture levels in place, thunderstorms will be capable of producing torrential rainfall in a very short amount of time. Rainfall rates of one to two inches per hour will be possible, and while many communities will receive beneficial totals of one to two inches, localized amounts of three to five inches could occur where storms repeatedly track over the same locations.

The greatest concern tonight into Thursday morning will be across the North Carolina mountains and foothills, where a Flood Watch is in effect. The combination of saturated mountain slopes, steep terrain, and repeated heavy rainfall could quickly cause creeks and streams to rise. Water can also collect rapidly in low-lying areas, poor drainage locations, and on roads that typically flood during heavy rain events.

As we move through Thursday, the slow-moving front will gradually sag south, allowing the heavy rain threat to spread farther into the foothills and portions of the western Piedmont. While not every community will experience flooding, it won’t take long for problems to develop wherever thunderstorms repeatedly move across the same area.

One positive change many of us will notice is the temperature. After weeks of hot and humid afternoons, widespread clouds and rain will keep temperatures running five to ten degrees below normal through Saturday. It will feel noticeably cooler, even though the humidity will remain high.

By late this weekend and into next week, the weather pattern finally begins to settle down. The stubborn upper-level trough responsible for this stretch of active weather will shift toward the Atlantic Coast, allowing a more typical late-July pattern to return. Afternoon temperatures will gradually warm back toward normal, and showers and thunderstorms will once again become the scattered, hit-or-miss variety that we’re accustomed to this time of year.

What You Need to Know

• Much-needed rainfall will provide welcome relief to drought conditions, but some areas could receive too much rain in a short period.
• Flash flooding is becoming the primary concern from tonight through Friday.
• Rainfall rates of one to two inches per hour and localized totals of three to five inches are possible where storms repeatedly move over the same locations.
• A Flood Watch is in effect for much of western North Carolina tonight through Thursday.
• If you encounter a flooded roadway, turn around. Water can rise much faster than expected, especially overnight when it’s difficult to judge depth or see washed-out pavement beneath the surface.
• Have multiple ways to receive weather warnings tonight, particularly if you live near a creek, stream, or in an area that is prone to flooding.

This is one of those weather setups where the rain will be a blessing for many but could quickly become dangerous for a few. The drought will certainly take a hit over the next couple of days, but we’ll need to closely monitor where the heaviest bands of rain develop because those locations could experience flash flooding with very little warning.