Over the weekend, parts of Louisiana and Mississippi saw more than a foot — 2 feet, in some neighborhoods — of rain from a stalled storm. NBC News reported that more than 20,000 people had been rescued and seven people have been killed.
The worst of the rain is over, but that doesn't mean the flooding is too.
"I'm still asking people to be patient. Don't get out and sightsee," Gov. John Bel Edwards of Louisiana told the Associated Press. "Even when the weather is better, it's not safe."
A handful of factors are coming together to keep the risks high over the next few days.
First, there are scattered pockets of rain in the forecast for the area this week. While 1 or 2 inches of rain usually wouldn't be a problem, with the ground already saturated there isn't anywhere for more rain to go.
A second factor is that floodwaters upstream are still making their way down toward the Gulf of Mexico. That's a huge amount of water, and there's a chance it won't all stay within the riverbanks as it makes its way south.
According to the Weather Channel, at least six rivers in the area have hit record-high levels — one river broke its record by as much as 6 feet. And parts of that same river, the Amite, weren't expected to hit their highest level until sometime on Monday.
Moreover, the National Weather Service believes these will be "long crest" events, potentially lasting days, rather than lighter crests that fade quickly.
"It's not over," Edwards warned, according to NBC News. "The water's going to rise in many areas. It's no time to let the guard down."
Even after floodwaters begin to recede, they could rise again because of backwater flooding, which occurs upstream when something blocks the flow of water downstream. The National Weather Service warned that backwater flooding was a risk along the streams that flow into the Amite River.
Taken together, these factors mean the National Weather Service is concerned about flooding continuing "during at least the first half of the workweek."
This flood is so unusual that experts aren't even sure precisely what will happen and where the water will go. "It's unprecedented and it's not anything anyone will know for sure," hydrologist Jeff Grashel told a local newspaper.
All of this is happening against the backdrop of climate change. According to one meteorologist's count, there have been at least eight 500-year rainstorms in the US within the past year — that means rainfalls so heavy they are predicted to occur only once every 500 years. This storm was so strong in part because it fed off unusually warm water in the Gulf of Mexico.
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