Why Did It Flood So Badly in Western North Carolina? Some Scientists Point to This Weather Effect
Hurricane Helene has become one of the deadliest storms to hit the U.S. in the last 50 years, with devastating flooding in Western North Carolina being the primary cause of the high death toll. Over 230 people have died so far, with half of those deaths occurring in Western North Carolina, and the numbers continue to rise as search efforts persist.
Helene hit the region as a tropical storm on Friday, Sept. 27, bringing torrential rain to an already waterlogged area. Rivers overflowed, sweeping communities away and turning them into dangerous debris.
The question is: why was the flooding so severe in this area?
The Role of the Orographic Effect
One explanation for the excessive rainfall lies in the orographic effect, a phenomenon that occurs when air masses are forced to rise over mountainous terrain, cooling and condensing water vapor, which leads to increased precipitation. According to Penn State, this process tends to focus rainfall on the windward side of mountains.
When Hurricane Helene encountered the Blue Ridge Mountains in Western North Carolina, the orographic effect intensified the storm’s impact. University of South Carolina Geography Professor Cary Mock explained that while fast-moving storms usually pose less of a rain threat, Helene was an exception due to the terrain. The mountains funneled heavy rain into rivers and streams, leading to extreme flooding in areas like Asheville, which is particularly vulnerable due to its bowl-like geography.
A Perfect Storm: Rainfall Stalling Before Helene
Even before Helene arrived, the region had already experienced significant rainfall from another storm system. According to David Easterling from the National Oceanic and Atmospheric Administration, a weather front stalled at the Appalachians just ahead of Helene, exacerbating the flooding by trapping moisture in the area.
Record Rainfall and River Flooding
During the storm, some parts of Western North Carolina recorded unprecedented rainfall totals between Sept. 24 and Sept. 28. Busick in Yancey County received the most, with 30.78 inches of rain, while other communities like Spruce Pine, Hendersonville, and Candler also saw over 15 inches.
The resulting river levels were historic. The French Broad River in Fletcher crested at 30.31 feet, while the Swannanoa River at Biltmore surpassed previous records with a peak of 26.1 feet. Many rivers throughout the region rose more than 10 feet above major flood stages, wreaking havoc on communities.
A Devastating Impact
The combination of orographic uplift, stalled weather systems, and saturated ground made Hurricane Helene’s flooding particularly catastrophic in Western North Carolina. The floodwaters destroyed homes, left thousands without power, and displaced entire communities, making recovery efforts ongoing and difficult.
The disaster serves as a reminder of the powerful forces of nature and the unique vulnerability of mountainous regions to extreme weather events like Helene.