Flood — Giles, Virginia

2023-05-29 to 2023-05-30 · near Narrows, Giles, Virginia

Event narrative

Wolf Creek at Narrows, VA (WOLV2), crested at 11.71 feet (9,650 cfs) at 13:30 pm EST on the 29th (1830 UTC) above the flood stage of 10.0 feet. The flooding was the result of between 2.5 and locally 4 inches of rain covering a large area of the headwaters, most of which fell between noon EDT on the 28th and noon EDT on the 29th. This is the 11th-highest documented crest of this gage, and the highest since February 2020. This event is nearly a 10-year event (10% Annual Exceedence Probability) per USGS StreamStats.

Wider weather episode

A deep, closed upper level low pressure system was observed over central Alabama on the morning of May 28th. The east winds around this low, allowed deep sub-tropical moisture from the Atlantic to move into lower Mid-Atlantic region. Areas of rain developed across the mountains by late morning, and gradually increased in coverage due to the sustained 25 to 30 knot (850mb) moisture inflow. Precipitable water values were observed in the 1.2 to 1.3 inch range through the day into the early morning hours of the 29th, which is around the 75th percentile for late May. Through the 28th into the early morning hours of the 29th, the upper low drifted eastward, allowing instability to increase across the central Appalachians as the associated pocket of cooler upper level temperatures approached. While Surface-based CAPE levels remained minimal during the event, Most-Unstable CAPE (MUCAPE) values were observed climbing across the mountains through the evening of the 28th into morning of the 29th, reaching into the 600 to 850 J/Kg range. Combined with orographic lift, this instability supported the development of low-topped thunderstorms with enhanced rainfall rates. As rainfall totals increased across the mountains and soils approached saturation, flash flood guidance values were lowered to under an inch at the 1- and 3-hour time periods.

The heavy rain then led to flooding of Wolf Creek and Walker Creek. Elsewhere, training cells across Floyd and Franklin Counties resulted in minor flooding of the South Fork of the Roanoke River, which brought the Roanoke River up to Action Stage as it passed through the Cities of Roanoke and Salem.

View location on OpenStreetMap → (37.3296, -80.8123)

Source: NOAA Storm Events Database, event_id 1098962. Narrative written by the NWS forecast office that issued the report.