Weather experts had predicted that Hurricane Helene would create a “once-in-a-generation” event in parts of the Appalachians, and this forecast sadly turned out to be true for the mountainous areas of western North Carolina, eastern Tennessee, South Carolina, and Georgia.

The tragic aftermath includes dozens of fatalities, hundreds of individuals reported missing, destroyed homes, damaged infrastructure, and damages totaling tens of billions of dollars.

Massive rainfall occurred before and during Helene’s arrival, leading to “the worst flooding ever recorded” in western North Carolina, as noted by Corey Davis, the state’s assistant climatologist, in a blog post on Monday.

The devastating flooding was the result of an unfortunate mix of climatic conditions, hydrology, and geographical features, according to experts speaking to YSL News on Monday.

Unprecedented volumes of rain fell over a stretch of more than 200 miles, transforming serene mountain streams into fierce torrents. The rushing waters flooded valleys, completely surrounding a hospital in East Tennessee and isolating entire communities in Western North Carolina.

Rain Predominantly Before the Storm

The rainfall from Helene would have triggered flooding in any area, but it was intensified by a stalled weather front over the Appalachians prior to the arrival of then-Tropical Storm Helene, as explained by David Easterling, a rain specialist at the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information based in Asheville, North Carolina.

On the afternoon of September 25, while Hurricane Helene remained a Category-1 storm over 500 miles south near Cancun, Mexico, it was already raining in the mountains due to a line of slow-moving showers linked to a stalled cold front, enhanced by moist air coming from the periphery of Helene.

This configuration between the cold front and Helene’s extensive circulation acted like a funnel, directing moisture from the warm Gulf of Mexico into the mountains prior to the storm’s arrival. As Helene traveled through the Gulf, it absorbed more moisture, resulting in even more rainfall.

Over a period of three days, rainfall totals varied widely, ranging from 6 to 30 inches across areas extending from North Georgia through western North Carolina, eastern Tennessee, and into Virginia.

Mountainous Regions Amplified Rainfall

The mountains themselves sometimes contributed to even higher rainfall totals as they create upward movements that enhance precipitation in thunderstorms, according to Easterling.

“It resulted in a continuous rainfall for at least 30 hours,” he stated, with some areas receiving more than 25 inches.

“All that water channels into smaller streams which feed into larger rivers,” he explained, which were then inundated with fast-moving water.

Challenging Terrain Contributes to Flooding

The terrain not only amplified the rainfall but also led to extreme flooding.

“The geography there – steep slopes and thin soil – is not suitable for heavy rainfall,” Russ Barton from NOAA’s National Water Center told YSL News. He pointed out that most infrastructure is located in the valleys, which become the main channels for floodwaters.

As all this water flowed into the major rivers, it wreaked havoc on everything nearby, said Easterling, who is among the many without electricity in the area.

High winds were toppling trees and causing power outages, while mudslides and landslides were also knocking down power poles throughout the region, he added.

“A single mudslide can lead to accumulations of 5 to 10 feet of mud. It closed I-40, which can destroy entire homes,” he mentioned. “The extent of the loss of life remains uncertain.”

Volume of Water

In the vicinity of Lake Lure, North Carolina, famous for its scenes in the film “Dirty Dancing”, the flow of Cove Creek surged to 32 times its normal capacity.

According to data from the U.S. Geological Survey, significant rainfall occurred on Tuesday and Thursday, leading to severe damage in the areas surrounding Lake Lure and Chimney Rock.

A water monitoring station located on the French Broad River in Asheville recorded a total of 12 inches of rainfall from Wednesday to Friday, as per USGS findings. The river also channels water from numerous creeks and streams to the north, which experienced even heavier rainfall.

The river’s flow rate surged by twenty times during the span from Tuesday to Thursday. As the water volume increased, it became more turbid, laden with mud and debris. Measuring instruments were not operational on Friday and Saturday, according to USGS data, but started up again on Sunday as water levels began to drop.

At that point, the swollen French Broad River was flowing at an impressive rate of over 240,000 gallons per second—enough to fill an Olympic-sized swimming pool in just 2.74 seconds.