“Many headline writers and meteorologists are justifiably turning to Genesis to describe an unprecedented deluge
‘Biblical proportions’ is an expression that headline writers use when trying to describe unprecedented rainfall or flooding. And “Biblical rain” was one tabloid’s response to a prediction that this month would be the wettest ever August. The near-disaster at Whaley Bridge was described in similar terms.
Meteorologists do sometimes refer to rainfall of biblical proportions, but only in exceptional cases. According to Genesis, the flood followed rain that lasted 40 days and 40 nights.
The term has been applied with some justification to a projected once-in-a-200-year storm in California known as the ARkStorm. This was extrapolated by scientists at the United States Geological Survey in 2011, based on storm in 1861/2 that dumped three metres of precipitation in 43 days.
In this type of storm, hot air and moisture from the tropical Pacific form atmospheric rivers that flow over the coast, producing a series of storms lasting several weeks.
ARkStorm is short for atmospheric river storm, but also refers to Noah’s ark. An ARkStorm would leave thousands of square miles submerged under up to six metres of water and require millions of people to be evacuated from their homes.
As there has not been such a storm in living memory, it seems almost unimaginable. But scientists continue to warn of the need for flood protection to handle rainfall of biblical proportions. ”
You may also find this article here: https://www.theguardian.com/news/2019/aug/16/weatherwatch-rain-biblical-proportions