Hurricane Helene Causes Over 40 Trillion Gallons of Rainfall in Southeast US

In the past week, the Southeast US experienced an unprecedented deluge, with over 40 trillion gallons of rain falling due to Hurricane Helene and a preceding rainstorm. This immense volume of water could fill Lake Tahoe once or the Dallas Cowboys stadium 51,000 times. If concentrated in North Carolina, it would create a water depth of 3.5 feet. The rainfall is equivalent to filling more than 60 million Olympic-sized swimming pools.

Ed Clark, head of the National Oceanic and Atmospheric Administration's National Water Center, expressed astonishment at the scale of this event. "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," he stated. The flooding has been catastrophic, with over 100 fatalities reported by officials.

Impact on Southeast US

Private meteorologist Ryan Maue calculated the rainfall using satellite and ground observations. He estimated that by Sunday, 40 trillion gallons had fallen across the eastern US, with 20 trillion gallons affecting Georgia, Tennessee, the Carolinas, and Florida due to Hurricane Helene. Clark independently verified these figures, noting they might even be conservative estimates.

Maue suggested that an additional one to two trillion gallons had fallen, primarily in Virginia. Clark highlighted that this rainfall exceeds twice the combined water stored in Lake Powell and Lake Mead, two major Colorado River basin reservoirs.

Weather Patterns and Storm Systems

The extraordinary rainfall resulted from a combination of storm systems. Before Helene's arrival, a low-pressure system stalled over the Southeast due to a jet stream disruption, bringing warm Gulf of Mexico moisture. A near-named storm also lingered along North Carolina's coast, dropping up to 20 inches of rain.

Kathie Dello, North Carolina's state climatologist, noted that Helene was one of the largest storms in decades. It carried significant rain because it was young and fast-moving before reaching the Appalachians. Kristen Corbosiero from the University of Albany emphasized that Helene's interaction with mountainous terrain exacerbated the situation.

Climate Change Considerations

Corbosiero and Dello pointed out that climate change is making storms wetter. A basic physics principle indicates air holds nearly 4% more moisture per degree Fahrenheit increase (7% per degree Celsius). The world has warmed over 2 degrees Fahrenheit (1.2 degrees Celsius) since pre-industrial times.

Meteorologists are debating how much of Helene's impact is due to climate change versus random factors. For Dello, climate change's influence is evident: "We've seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer."

North Carolina weather officials recorded a top measurement of 31.33 inches in Busick town, with Mount Mitchell receiving over two feet of rain. Clark remarked on the increasing frequency of measuring rainfall in feet since events like Hurricane Harvey in 2017.

The interaction between mountains and storm systems worsened conditions by extracting more moisture from the air. This phenomenon contributed significantly to the flooding experienced during this event.