Flash Flood — Montgomery, Virginia

2023-09-09 · near Blacksburg Vpi Arpt, Montgomery, Virginia

Event narrative

A photo taken by a member of the public shows that Cedar Run flooded out of its banks up to a foot deep across Ellett Road at both locations where the road crosses over the Cedar Run. The flooding was due to 4 to 5 inches of rainfall within a 2-hour period in the headwaters of the run. No damage was reported to the road and it was reopened after flooding receded.

Wider weather episode

An upper trough situated from the Great Lakes through the Tennessee Valley provided the instability to support very slow-moving showers and thunderstorms that drifted across the central Appalachians into the lower Mid-Atlantic. During the afternoon of the 9th, a surface trough had developed from Surry County, NC northward through Montgomery County, VA into southeast West Virginia, providing the low level convergence needed to support prolonged thunderstorm activity. A southerly wind flow carried deep moisture northward from the Carolina coast during the afternoon, with precipitable water values observed in the 1.5 to 1.6 inch range across Montgomery County, while surface-based CAPE values were observed in the 1,000 to 1,200 J/Kg range. Steering winds were less than 10 knots from the south, leading to slow storm movement. Several personal weather stations indicated that the vast majority of rainfall occurred during a 2-hour period beginning around 1 PM EDT, with rainfall falling at rates of 4 to 6 inches per hour. CREST Unit Streamflow in the town of Blacksburg near the headwaters of Cedar Run peaked at 19Z at around 1,000 cfs/sec/mi^2, while the three-hour Average Recurrence Interval was nearing a 200-year event.

View location on OpenStreetMap → (37.2087, -80.3985)

Source: NOAA Storm Events Database, event_id 1119846. Narrative written by the NWS forecast office that issued the report.