Report: Helene Dumped The Equivalent Of The Entire Contents Of Lake Tahoe On Southeast U.S.

United States rainfall from September 24 to 29. Click
on the map to make it bigger and easier to see.
That bright purple splotch in western North
Carolina represents about two feet of rain. 

 Hurricane Helene combined with the "predecessor rain event" associated with that storm in the Southeast dumped 40 trillion gallons of water on the region.  

The Associated Press reports:

"That's enough to fill the Dallas Cowboys stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina, that much water would be 3.5 feet deep. It's enough to fill more than 60 million Olympic-size swimming pools."

It would also take 619 days for that amount of water to flow over Niagara Falls, on average.

The rainfall amount was calculated by meteorologist Ryan Maue, a former NOAA chief scientist. 

Other meteorologists checked Maue's work, and said his work looks pretty damn accurate. If anything, Maue might have underestimated the rainfall a little. 

The AP reports: 

"'That's an astronomical amount of precipitation,' said Ed Clark, head of the National Oceanic and Atmospheric Administration's National Water Center in Tuscaloosa, Alabama. 'I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky."

The town of Busick in western North Carolina received 31.33 of rain. Other locations not far from Asheville received more than two feet of rain. 

Also, this was the second mega-rainstorm parts of North Carolina within just two weeks. On September 15-16, a stalled storm along the North Carolina coast that tried and failed to turn into a tropical storm still managed to dump 20.81 inches of rain on Carolina Beach and a foot to a foot and a half of rain in southeastern part of that state. 

Obviously with that much rain, extensive flooding was reported in that area. 

We should expect to see more and more of this in the coming decades as climate change continues to intensify. Warmer air can hold more moisture, and under the right conditions, can dump ever heavier amounts of rain. 

This is leading to more frequent and worse flooding in many areas. Us Vermonters know a thing or two about that given the events of the last two summers. 

Maue and others point out there were mega-floods well inland from coastal areas associated with both tropical and non-tropical systems well before climate change was a thing. 

That is true. Western North Carolina had a highly destructive flood like Helene back in 1916, though that one wasn't quite at the level of the one they just experience. 

In August, 1969, Hurricane Camille smashed ashore in Mississippi as a deadly Category 5 storm. It was one of the most powerful hurricanes ever to hit the United States. The remnants of Camille moved on to the mountains of western Virginia, where it dumped up to 27 inches of rain. That unleashed flooding that killed at least 150 people.   

Even here in Vermont, an offshore former tropical storm fed deep moisture into the state, creating the Great Flood of 1927.

So yes, big floods have always occurred. But it's happening more often and these things are getting wilder.

Associated Press again:

"Before 2017's Hurricane Harvey, 'I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,' Clark said. 'And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We're seeing events year in and year out where we are measuring rainfall in feet."

For now, the nation is getting a brief break. Forecasts for the Lower 48 over the next two or three days show the least flood threat overall in months. However, southern and central Florida could see torrential rains and flooding starting early next week from a potential weak but slow-moving tropical system that's forecast to be in that area.