Flood in Smyth County, Virginia

The South Fork Holston River at Riverside near Chilhowie (SHLV2) crested at 10.87 feet at 20:00 UTC/4:15 PM EDT on Sept. 27th due to heavy rain associated with Tropical Cyclone Helene. This is a new Flood-of-Record for this gage, with records dating back to October 1920. The discharge of 11,300 cfs for 10.87 feet was estimated through extrapolation as this stage is above the rating curve. This discharge would be greater than a 500-year Average Recurrence Interval (ARI), or a 0.2% Annual Exceedance Probability per USGS StreamStats. The flooding was the result of between 10 and locally 16 inches of rain that fell in multiple rounds across the basin between the 25th and 27th, with 3-day totals across most of the upper basin exceeding an 1,000-year ARI per NOAA Atlas 14 Point Precipitation Frequency estimates.

Hurricane Helene made landfall in Florida as a powerful Category 4 hurricane late Thursday, September 26, and moved quickly northward into the southeastern states, and then turned slightly northwestward towards the southern Appalachian Mountains overnight into Friday morning, weakening as it moved over land. Helene's intensity and fast forward motion led to impacts being felt well inland, from the Florida Big Bend area into the Appalachians, almost only 12 hours after landfall, and there was extensive damage in southwest Virginia. Widespread cellular service and power outages, some lasting for several days, occurred as high winds downed thousands of trees across the region. Winds gusted as high as 55 mph to 65 mph in southwest Virginia. There were three confirmed tornadoes associated with the remnants of Hurricane Helene in the Piedmont of Virginia. Flooding impacts from Hurricane Helene were extensive across the area, and were exacerbated by a predecessor rainfall event that occurred a day before Helene reached the region, which brought six to eight inches of rain to the mountains prior to the arrival of the remnants of Helene. The three day rainfall totals associated with the remnants of Hurricane Helene were highest Grayson and Smyth Counties, where observations of 10 to locally 15 inches of rain were recorded. The Piedmont of Virginia received much less rain, between one and two inches, with a couple areas around three inches. Total economic losses for Virginia, which include Virginia's agriculture, forestry, and other industries, are expected to range between $416 million and $630 million per an economic analysis released by Virginia Tech researchers.