Flash Flood — Montgomery, Virginia

2023-09-09 · near Merrimac, Montgomery, Virginia

Event narrative

A National Weather Service employee observed flood waters flowing across North Franklin Street up to 1 foot deep near the intersection with Red Oak Drive. No damage was observed to the road, and it was reopened after the 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 → (37.1716, -80.4213)

Source: NOAA Storm Events Database, event_id 1119847. Narrative written by the NWS forecast office that issued the report.