Flood — Roanoke (c), Virginia

2015-09-29 to 2015-09-30 · near Roanoke, Roanoke (c), Virginia

Event narrative

The Roanoke River flooded through the city of Roanoke due mainly to the very heavy rains across the upper basin. Rainfall in the city was generally around 1 inch during the day but up to 4 inches fell across the headwaters in Montgomery County. The USGS gage and NWS forecast point at Walnut Street (RONV2) rose very rapidly, reaching flood stage (10 ft) by early afternoon and cresting at 14.40 ft in the Moderate Flood Category and the 10th highest stage on record (data at the current location since 1937). The recurrence interval per USGS data on the flooding at the Roanoke gage indicated approximately a 10-year event (0.1 annual exceedance probability). Several roads close to the Roanoke River were closed but no substantial damage was reported. Water rescues from three vehicles on Bennington Street were performed during the evening of the 29th.

Wider weather episode

One of the most high-impact flood/flash flooding episodes in recent years in the Blacksburg Hydrologic Service Area (HSA) developed over a several day period but culminated September 29th. An unusual weather pattern became established around September 25th with very slow-moving and strong high pressure building across New England and low pressure over the southeastern U.S. combining to bring strong easterly flow into the southern Mid-Atlantic along with abundant moisture. Rainfall ending 12z on the 25th was generally confined to the southern portions of the HSA with up to 1 inch in parts of the North Carolina piedmont into southside Virginia. The rains became much heavier and widespread over the next two days with 1 to 4 inches ending at 12z on the 26th and another 1 to nearly 5 inches ending at 12z on the 27th. Over the next five days rainfall was nearly constant in some areas with pulses of heavier rainfall but with the heaviest amounts concentrating across the VA Blue Ridge mountains, mainly in Patrick, Floyd, Roanoke, Henry and Franklin counties. The maximum 5-day rainfall totals ending at 12Z (8 AM) on the 30th ranged from 10 to 16 inches in parts of Patrick and Floyd counties. Some of the higher totals equate to anywhere from a 100 to 500-year event per NOAA Atlas 14. The extremely wet soils set the stage for the severe flash flooding early on September 29th into the afternoon. Several bands of intense rainfall tracked across parts of the same counties mentioned above and also including Montgomery County over a 6 to 12 hour period from 0200 LST to 1400 lST (06z-18z) prompting the issuance of two Flash Flood Warnings for parts of eight counties and several cities at 943 AM (EDT) and 1019 (EDT) AM. It was difficult to differentiate between the onset of flash flooding from the longer duration flooding that was developing or underway as well. No matter the type, by mid-morning numerous reports of flooding and several high water rescues had been reported across a wide area, but most notably in parts of Patrick, Floyd, Montgomery, Roanoke and Henry counties. Local states of emergency were declared in Floyd and Patrick counties due to the widespread flood impacts with water rescues, some homes damaged and dozens of roads closed due to flooding or trees brought down in the saturated soil.

View location on OpenStreetMap → (37.2593, -79.9911)

Source: NOAA Storm Events Database, event_id 602077. Narrative written by the NWS forecast office that issued the report.