Flash Flood in Monroe County, West Virginia

Trout Run Road was flooded and impassible due to Trout Run overflowing its banks several inches deep across the road. A slow-moving thunderstorm produced between 2.5 and 3.5 inches of rainfall within most of the Trout Run watershed during a 60 to 75 minute period, or in excess of a 100-year Average Recurrence Interval for a 1-hour duration per MRMS FLASH. The 1-hour QPE to FFG ratio was close to a 3, or nearly 3 times the 1-hour rainfall needed to produce flash flooding. CREST Unit Streamflow indicated flows in the upper part of the basin reaching around 700 cfs/mi^2, a strong indicator of flash flooding.

An upper level trough passed across the central Appalachians during the afternoon and evening of May 18th, triggering widely scattered showers and thunderstorms to the north of a stationary front stretching across northern North Carolina. Upper level winds ahead of the trough were light. Moisture was abundant, with precipitable water values ranging from 1.2 to 1.3 inches across southeast West Virginia, while surface dewpoint temperatures were observed in the mid 60s. Mixed Layer CAPE (Convective Available Potential Energy) was in excess of 1,000 J/Kg during the afternoon and evening. The thunderstorms that developed during the afternoon and evening were localized but extremely efficient at producing rainfall, with rates within several storms exceeding four inches per hour. They were also slow-moving, allowing the storms to remain over locations for extended periods of time.

In the Town of Bluewell, heavy rain began falling at around 6:30 PM EDT and continued through around 8:30 PM EDT before exiting the area. Rainfall rates were estimated to be between three and four inches per hour, with a radar-estimated total of nearly four inches. By 8:40 pm EDT, CREST Unit Streamflows had risen to over 540 cfs/mi^2 in the Bluewell area, with the FLASH 3-hour average recurrence interval indicating a 200+-year event. The 3-hour QPE/FFG ratio over the town indicated that rainfall was between 2 and 2.25 times that of the 3-hour flash flood guidance. Some of the more flood-prone areas around Bluewell experienced flash flooding, including along Airport Road and Coal Heritage Road, which have been noted to experience flooding in the past.