How long it took 50 inches of rain to accumulate 4 mo. 8 mo. 12 mo. 16 mo. 20 mo. 2 yr. 3 yr. 5 yr.

Parts of Houston might receive 50 inches of rain before the storm ends. That's equivalent to all of the precipitation from the past in the area — in just one week.

Hurricane Harvey has already dropped a staggering amount of rain over parts of the Houston metropolitan area. Before it is done, some places might get 50 inches.

It’s a historic amount of precipitation. The National Weather Service characterized the rainfall as “unprecedented” and “beyond anything experienced.” It is hard to comprehend how much rain is falling on southeast Texas. Here’s one way to think about it: Most parts of the country have not received 50 inches of precipitation over the last year. Fifty inches is more rain than Houston gets in a typical year — in just a few days.

Or consider our best guess for where you're reading this article — the area: It has taken for 50 inches of precipitation to accumulate there. (Use the search box near the top of this page to see the amount of time for other cities and towns.)

The map at the top of this page shows this relationship across the contiguous United States, using precipitation data from the National Oceanic and Atmospheric Administration. Colors reflect the approximate amount of time it has taken to accumulate 50 inches of precipitation. The places most affected by Harvey are expected to get more rain than many parts of the country did over the last year.

But even the big tallies don't quite convey the scale of Harvey’s rainfall. The storm that currently holds the record for wettest tropical cyclone in the continental United States — Amelia — dumped prodigious volumes of water over a much smaller and less populated area in 1978.

Tropical Storm Allison, the sixth-wettest tropical cyclone, hammered the Houston metro area in 2001 with seemingly similar 30-plus-inch rainfall. But Allison’s heavy rains in the Houston area were confined to a narrow band. Parts of the county that contains Houston, Harris, didn't receive even five inches. Everywhere in Harris County has received at least 20 inches under Harvey.

People have tried to convey the scale of Harvey’s torrential rains by using the volume of rainfall, not the accumulated precipitation in a specific spot. Harvey might deliver 20 trillion gallons of rain by the time the storm is through. That may be even harder to comprehend, but it’s as much as:

• A cube of water about 2.5 miles high and wide, to borrow from The Washington Post's depiction on Sunday.

• About 10 percent of Lake Erie.