(left) The weather conditions leading to extreme pre-hurricane rainfall across the Southern Appalachians during Helene. Converging winds spun a plume of moisture off the eastern side of Helene. That plume was vacuumed inland by areas of low pressure in the upper atmosphere. Inland, it met first the mountains and then the front edge of a colder air mass. Forced high into colder parts of the atmosphere, the tropical moisture condensed into multiple rounds of heavy rain. (right) Hurricane Helene was still in the Gulf of Mexico on September 26, 2024, but it was feeding moisture into rain clouds that stretched hundreds of miles north. Climate.gov illustration adapted from a schematic by J. Cordeira for the Center for Western Weather and Water Extremes (CW3E). NOAA GOES-16 satellite image.