Heavy Rain in Roanoke (c) County, Virginia

The ASOS at the Roanoke-Blacksburg Regional Airport (KROA) recorded at daily rainfall total of 4.27 inches, most of which fell between 6:50 pm EDT and 8:50 pm EDT. This was a new daily rainfall record for August 21, surpassing the old record of 1.73 set in 1960. This was also Roanoke's 3rd highest 1-day total for any day in August, and the 13th highest 1-day total on record, with records dating back to February 1912. This total had a nearly a 500-year average recurrence interval for a 2-hour period per NOAA Atlas 14 Point Precipitation Frequency estimates.

A thunderstorm developed over the City of Roanoke just before 6:45 pm EDT on August 21st, initially producing rainfall rates to nearly 5 per hour. Though the storm gradually weakened, it remained anchored over primarily the western half of the city through around 8:15 pm EDT before finally pushing away to the south. While nearly all of the city received at least 2 inches of rain, the highest totals were over the Peters Creek basin, where a 4 to 5 bullseye stretched from the Roanoke-Blacksburg Regional Airport (KROA) westward to S. Electric Road. Both the airport and a personal weather station observed rainfall totals at the 1-hour and 2-hour durations that were 500-year rainfall events per NOAA Atlas 14 Point Precipitation Frequency estimates. By 8:00 pm EDT, CREST Unit Streamflow near the airport had peaked at just over 1,600 cfs/mi^2, with much of the western half of the city observing values ranging from 550 to 950 cfs/mi^2. FLASH 1-hour Average Recurrence Intervals peaked near Electric Drive at just under a 200-year event at 7:46 pm EDT. Due to the rapid flooding of Peters Creek Road that runs alongside Peters Creek, the occupants of numerous vehicles required swift water rescues from emergency services personnel. A Flash Flood Warning with a Base tag was issued at 7:29 pm EDT for the City of Roanoke, which was upgraded to a warning with a Considerable tag at 7:52 pm EDT when reports of swift water rescues began to come in. After coordinating with the Emergency Manager of the City of Roanoke, the warning was upgraded to a Flash Flood Emergency with a Catastrophic tag at 9:02 pm EDT.