Weather Blog

How much rain in Seattle this week? Millions of tanker trucks' worth

How much rain in Seattle this week? Millions of tanker trucks' worth

We all know Seattle gets a lot of rain, but have you ever thought of just much water really falls in a big rainstorm?

Local engineer Dale Smith had the burning question pop into his head when he read about a statistic that says our "Pineapple Express" type rain storms transports an amount of water vapor equal to between 7.5 to 15 times the average flow of liquid water out of the Mississippi River.

His quest: How many tanker trucks would it take to haul enough water to cover all of King County with 1 inch of rain -- roughly the amount of total rain expected in the Seattle area through the weekend.

(Start formulating your guesses now)

10,000? A million? A billion?

For his base, he's using the double tankers that you see filling up gas stations -- those carry 8,000 gallons of liquid.

King County is 2,307 square miles, which translates to just over 9 trillion square inches. (9.261 trillion to be fairly exact).

Now that we know how much land we need to cover, we need the water. One U.S. Gallon is 231 cubic inches -- a cubic inch of water on a square inch of land would cover that parcel with 1" of water.

So take 8,000 gallons of water in one truck, multiply by 231 and we find each tanker can carry 1,848,000 cubic inches of water.

Thus, just how many trucks would it take to cover King County with 1" of rain?!?!

Just over 5 million! (5,011,595. Or just call it 5 million and leave a few driveways dry.)

Smith says King County has about 2 million people, so every person -- even the kids -- would have to make 2.5 trips to Puget Sound or the ocean to fill a truck and bring it back.

But what about covering all of Western Washington? The rain doesn't just stop on the county lines, you know!

That is 96.348 trillion square inches, and would take 52.1 million trucks, or about 10 trucks per person. Think of the amount of tanker trucks we'd need to supply the gas for all our water trucks!

Instead, it's provided for free by Mother Nature.