Heavy Rain — Grayson, Virginia

2024-05-22 · near Rugby, Grayson, Virginia

Event narrative

A personal weather station (Weather Underground: KVAMOUTH12) recorded a 2-hour rainfall amount of 2.54 inches. This amount has between a 10-year and a 25-year Average Recurrence Interval per NOAA Atlas 14 Point Precipitation Frequency estimates. Rainfall rates were measured to be as high as 3 inches per hour at times.

Wider weather episode

Multiple intense thunderstorms developed with the passage of an upper level disturbance during an afternoon of strong daytime heating. Abundant sunshine and above normal warmth resulted in surface-base CAPE (Convective Available Potential Energy) values ranging from 2,000 to 2,500 J/Kg for areas west of the Blue Ridge in western Virginia. Precipitable water values were estimated to be in the 1.2 to 1.3 inch range as southerly wind flow tapped deeper moisture pooling ahead of an approaching cold front to the west.

Flash flooding occurred in two separate areas of Grayson County as intense storms began to train over the same area. One storm produced between 3 and 4.5 inches to the east of Troutdale, while the other produced 4 to 5 inches near the community of Rugby, each during a 2 to 2.5 hour period. MRMS FLASH indicated rapid responses to the heavy rain, with CREST Unit Streamflows ranging from 500 to locally over 1,000 cfs/mi^2. With both storms, 1-hour, 3-hour and 6-hour ARIs (Annual Recurrence Intervals) maxed out at 200-year events, and estimated rainfall was more than double flash flood guidance for the area at the 1-hour, 3-hour and 6-hour intervals.

View location on OpenStreetMap → (36.5930, -81.4560)

Source: NOAA Storm Events Database, event_id 1168751. Narrative written by the NWS forecast office that issued the report.