Weather Blog

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

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

We all know the Willamette Valley 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 the Willamette Valley area with 1 inch of rain -- roughly the amount of total rain expected in the 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.

Going with just the Portland metro-area counties of Multnomah, Washington and Clackamas, those total 3,071 square miles, which translates to just over 12.3 trillion square inches. (12.3285 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 those three counties with 1" of rain?!?!

6.67 million! Add in Clark County for our Vancouver friends and it jumps to 8.1 million.

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.