Western North Carolina Sets Record in May 2018 for Wettest Month

May of 2018 was a very wet month for much of the East Coast. Well above normal precipitation was recorded from Florida to Pennsylvania. A large long-wave ridge dominated the CONUS, but short-wave troughs were in evidence. During the middle of the month, a low pressure system originated in the Gulf of Mexico and slowly moved into the Southeast bringing widespread rainfall from Florida to Pennsylvania. At the end of the month, tropical storm Alberto moved out of the Gulf of Mexico up the Ohio Valley bringing additional rain to an already saturated area. Reflecting these events, Asheville, North Carolina received 14.68 inches of rainfall for the month, which exceeded the previous May record by 5.5 inches and also surpassed record rainfalls for all other months. The two storms were not record producing events unto themselves, but their combined rainfall set the record for the month. The French Broad River which flows through Asheville, rose rapidly to over 10 feet for the first storm, and with the saturated soils rose again during Alberto. An inundation model developed by Riverside Technology, inc. showed the extent of the inundation through Asheville to 30 miles downstream, south of the city. An analysis of CoCoRaHS observations of surrounding counties showed the record Asheville precipitation was no fluke. An average of ten CoCoRaHS stations with 31 days of observations in Henderson County just south of Asheville is 18.9 inches of rain. Western North Carolina, while not densely populated, has the highest peaks in the east. The terrain is characterized by steep slopes bordering river valleys. Important roadways wind their way along rivers and streams adjacent to steep slopes. The heavy rains caused massive mudslides of these some steep slopes. More than 50 roads across 13 counties were closed at one point. In one example, an important commuter roadway was buried, requiring the North Carolina Department of Transportation two months to reopen and then with just one lane of the highway. During Alberto, I-40 was closed east of Asheville due to a landslide. Two thousand residences were evacuated below the Tahoma dam, east of Asheville, because of concern for its failure. Power was lost to several thousand homes. Multiple water rescues were reported in several counties.

Five people perished due to the storms. U.S. Department of Agriculture declared four North Carolina counties as natural disaster areas, and the USDA Farm Service agency opened its emergency loan program for those and neighboring counties. The U.S. Small Business Administration is opening its loan programs to assist farmers, small businesses and non-profits affected by the disaster. This talk will address both the meteorological and hydrologic aspects of the storms, and the impacts on agriculture and transportation caused by the heavy rains and the resulting flooding and landslides. The talk will also address what was learned about observing, forecasting and communicating the event based on discussions with the local WFO forecast staff and the National Hurricane Center final report on Alberto.