Intense, localized thunderstorms produced world-record level rainfall (~20 inches in 2.5 hours!) near Rockport, WV July 18th-19th, 1889. Applied Weather Associates (AWA) used its Storm Precipitation Analysis System (SPAS) to analyze this event after gathering all observational and anecdotal information. This storm resulted in unprecedented flooding and more than 100 fatalities. The extreme of this event resulted in large amounts of documentation to capture the tragic events as they unfolded amongst the communities impacted by the storm. Interestingly, this storm occurred just over a month after the infamous Johnstown, PA deadly flood demonstrating a connection between the weather patterns and unique topography in this region. This storm is also similar to world-record type rainfalls that have repeatedly been observed in this area, including Smethport, PA July 1942, Simpson, KY July 1939, and Johnson City, TN June 1924.
The results of the unique storm reconstruction will be instrumental in determining local storm PMP depths for short duration and small area-sizes in the ongoing North Carolina statewide PMP study. In addition, AWA will be checking the sensitivity of this storm analysis against our surrounding statewide and site-specific PMP studies.
A combination of first-hand accounts of the event, observed precipitation data, and AWA’s SPAS analysis were able to capture the tragic event as it unfolded in time and space. The storm analysis was used to estimate Depth Area Duration (DAD) and temporal information to aid in Probable Maximum Precipitation (PMP) development for dam design and evaluations.
It is likely that this storms’ hourly precipitation rivaled known world record precipitation intensity for one and two-hour durations. SPAS DAD tables show average precipitation depths over a ten square mile area greater than 12 inches for one hour and over 20 inches for two hours.
This presentation will detail the importance of capturing the impacts of these types of rare events in all forms to help inform detailed reconstruction of extreme rainfall for dam safety. This is critical because this type of storm can be controlling of PMP depths and helps to fill in data gaps that exist for short durations. This analysis demonstrates how valuable anecdotal and first-hand accounts can be when combined with AWA’s expertise in storm analyses and rainfall reconstruction. This adds another significant storm to the AWA’s extensive storm database of nearly 1000 extreme storm events that are used in PMP development for dam design and evaluations.
