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Between September 23 and 28, the highest 3-day rainfall totals across the higher elevations of the southern Appalachian Mountains were so extreme that the statistical chances of them being exceeded in an any given year were 1 in 1,000 (black areas). Statistically, this is the same as saying that averaged over long periods of time, a 3-day rainfall event so extreme would only occur on average (not literally!) once every 1,000 years. NOAA Climate.gov graphic, adapted from original by NOAA's National Weather Service.