Parts of the southern Appalachians are dealing with excessive rainfall and flooding after more than 7 inches fell through early Wednesday in parts of the Carolina Piedmont. Continued downpours and thunderstorms will yield additional flooding over parts of the Southeast and the southern Ohio Valley, with some locations likely to close in on a foot of rain when all is said and done.
With upward of half a foot fallen and another 4 or 5 inches on the way for some, the National Weather Service Weather Prediction Center has outlined a “high risk” of flash flooding along the east slopes of the high terrain in the western Carolinas and southwest Virginia. There’s even a chance of a few mudslides or landslides. The Roanoke area is in one of the high risk zones through Thursday morning, based on forecasts issued Wednesday afternoon. High risk days like today tend to be associated with the vast majority of flood-related damages, and nearly half of flood-related fatalities each year, according to recent research.
The tropical torrents stem from a “cutoff low,” or an upper-level low pressure system, characterized by cold air and rotating winds aloft, that’s pinched off from the jet stream’s winds to the north.
Moisture wrapping northwest along its periphery is focused by the Appalachians and channeled into heavy downpours. And when the upper-level low stalls and parks for several days, those heavy bands of rain hardly budge.
The rains began Monday in most areas, coming as a burst of heavy showers and downpours interspersed by periodic lulls. They continued off and on through Tuesday, with impressive totals equaling what would normally fall in several months. Polk County, N.C., emerged atop the list early Wednesday, with up to 7.5 inches tallied in just 24 hours in the town of Columbus. Elsewhere nearby, totals of 6 to 7 inches were logged.
A one-day rain total of 6.62 inches had come down by dawn Wednesday north of Greeneville, S.C. Flash flood warnings were in effect for the area Wednesday morning as continued rounds of thunderstorms moved across the area.
The mountainous terrain of the Appalachians helps focus the moist southeasterly flow like an atmospheric cistern, funneling it into persistent downpours that target the same areas.
Another widespread 2 to 4 inches is likely across the lower Appalachians and extreme southern Blue Ridge, especially west of Interstate 77 and between Interstates 81 and 40. Localized 6 inch amounts are likely. That includes places like the Pisgah and Cherokee national forests.
The National Weather Service in Greer, S.C., also noted that the sodden grounds will make it easy for trees to topple even in low winds.
Flood concerns are exacerbated by saturated soils unable to absorb much more water. As of late April, soil moisture in the Carolina Piedmont was in places nearing its 99th percentile.
Most of the South, Southeast and Tennessee Valley away from the Gulf Coast and the Carolina Low Country has seen at least 8 inches more than normal in the past six months.
Rain will continue off and on across the area through Thursday, beginning to taper back as the instigating upper-level disturbance weakens into Friday. There is also a marginal risk a tornado or two could touch down associated with the ribbon of thunderstorms, but the threat is low.
Andrew Freedman contributed reporting.