The system that stretched from Texas to the Canadian Maritime provinces had prompted several emergency declarations even before the dangerous storms arrived.
All this was accompanied by swathe of rain extending from Texas through Arkansas to Kentucky and Ohio, bringing with it major flooding. The Ohio River has overcome its banks in Cincinnati, Ohio and Louisville, Kentucky, among other cities.
The bloated river will feed that excess water into the Mississippi River over the coming days, taking the flood risk downstream.
Nevertheless, the most significant flooding so far has been in southwest Michigan, northwest Indiana, and northeast Illinois, where heavy rain fell on a snowpack that completely melted, releasing meltwater equivalent to another 25mm of rain. The rain also came with higher temperatures.
Nbcnews.com reports on several cities across the central and southern part of the US experiencing temperatures of at least 10 degrees Celsius above average on four of the five wet days. Warm air can hold more water vapour, which can produce more rain. This flow of unusually moist air came northwards from the Gulf of Mexico, where water temperatures were and are about one degree Celsius above average.
Every degree Celsius that the air warms up increases the amount of water vapour it can hold by seven percent. The average moisture content of the atmosphere has already increased by about 4 percent since the 1970s. This increase has been attributed, in part, to human-caused global warming. More and greater floods seem an inevitable consequence.