Heavy Rain — Alleghany, North Carolina

2023-07-15 to 2023-07-16 · near Roaring Gap, Alleghany, North Carolina

Event narrative

A personal weather station (Weather Underground: KNCGLADE22) recorded 7.12 inches of rainfall in a 6-hour period, with prolonged rainfall rates of 3 inches per hour. This event was nearly a 500-year rainfall event per NOAA Atlas 14 precipitation frequency estimates. Runoff from this location flows into Brush Creek.

Wider weather episode

Thunderstorms developed, with some becoming severe, as a wave of low pressure passing along the front over western North Carolina served to increase 925 mb and 850 mb winds into the 20 kt-25 kt range from the south, tapping into deep moisture over the eastern Carolinas. By 8 pm EDT, precipitable water values across northwest North Carolina had risen as high as 2.1 inches, which is around 2 standard deviations above normal for mid-July per NWS gridded climatology estimates. Instability was also observed to be extremely high, with surface-based CAPE values in the 2,500 to 3,000 J/Kg range. In Alleghany County, a thunderstorm produced over 7 inches of rain within a 6-hour period across the headwaters of Glade Creek, with prolonged rainfall rates at 3 inches per hour. MRMS FLASH CREST Unit Streamflows registered between 600 and 800 cfs per mi^2 due to this rainfall, while 3-hour QPE/FFG indicated that the rainfall was between 2.25 and 2.5 times of the 3-hour flash flood guidance.

View location on OpenStreetMap → (36.4130, -81.0040)

Source: NOAA Storm Events Database, event_id 1125366. Narrative written by the NWS forecast office that issued the report.