Here’s what made Helene’s catastrophic flooding even worse
A predecessor rain event saturated the ground before Helene’s arrival.
NASHVILLE, Tenn. (WSMV) - Days of rain before Helene, combined with tropical downpours brought catastrophic flooding to Eastern Tennessee and Western North Carolina.
Before Helene’s arrival in Eastern Tennessee and Western North Carolina, there was already heavy rain ongoing. A stalled front caused slow-moving showers for days. Tropical downpours on top of already saturated ground made things much worse.
This was a classic example of what is known as a predecessor rain event (PRE). PREs occur when a large batch of sustained heavy rain forms ahead of a tropical system’s arrival.
PREs generally occur about 36 hours ahead of a tropical system’s arrival and as much as 600 miles poleward of the center of the storm. PREs do not form at the coast but do form inland.
The stalled front, that was generating this predecessor rain event, led to 7-11″ of rain before Helene ever impacted the area. Once the center of Helene moved over these areas in the mountains, just as much rain fell but in an even shorter time frame.
Numerous rivers in Eastern TN and Western NC saw record crests due to extreme rainfall amounts. Busick NC received 31″ of rain, Spruce Pine recorded over 24″ of rain with similar amounts in Eastern TN.
So much rain fell in areas like Unicoi and Greene counties in Eastern Tennessee that TVA officials feared Dams would break leaking even more devastation of those areas. The dam remained intact and TVA exited its emergency conditions.
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