Heavy Rain in Lexington (c) County, Virginia

An automated weather station (Weather Underground: KVALEXIN35) observed a 2-hour rainfall total of 2.27 inches, which is between about a 25-year rainfall event per NOAA Atlas 14 point frequency estimates for this duration. Rainfall rates during this 2-hour period remained above 1 inch per hour for about 65 minutes.

Deep tropical moisture associated with the remnants of Tropical Storm Nicholas was lifted northward ahead of a strong cold front. Precipitable water values ranging from 1.9 to 2.2 inches were carried into southern Virginia during the evening of the 21st. Warm rain processes produced localized rainfall rates of 2- to 3-inches per hour during the late evening of the 21st into early on the 22nd, enhanced by orographic lift up the Blue Ridge. FLASH (Flooded Locations And Simulated Hydrographs Project) data indicated bands of rainfall were producing amounts of 1.5 times flash flood guidance across Floyd and Montgomery Counties, with 10-year annual return intervals in spots near the crest of the Blue Ridge before rainfall diminished toward dawn. During late afternoon into the evening on the 22nd, a line of thunderstorms developed further east as the cold front advanced across the mountains. The line of storms stalled across portions of Botetourt and Bedford Counties, while CAPE values of 1,500 J/Kg, provided enough instability to support rainfall rates of 2 to 3 inches per hour. Despite antecedent dry conditions, the areas heavy rain was sufficient to produce localized flash flooding.