Weather Blog

Can we blame my daughters for the rainy week?

Can we blame my daughters for the rainy week?
4 cups of water left over after my kids' bath on Tuesday night.

Summer begins Thursday, but it sure doesn't look the part. But could my young daughters have had a hand in making it rain this week?

I noticed Wednesday morning after their bath was done that they had left four small cups filled to the brim with water. It jogged a memory from when I was a kid that one time I left the bath water in overnight and then two days later, we had a really big rainstorm and I wondered: Did my leaving the water in the bath help give more rain in the clouds? (Never mind that the water was still mostly in the tub as you would expect and not spontaneously evaporated, but I think I was 9...)

So being the scientist that I am and, now that school's out, had a few extra minutes this morning to run around, I decided to find out: Could my daughters' leftover water contribute in any way to the current rainy pattern?

Tongue firmly in cheek, I set out to measure how much water they had left behind in the cups. (Puzzled daughter: "Daddy, why are you running downstairs with a pitcher full of water?" Me: "It's for science!... and our Pyrex are in the kitchen.")

It turns out they had saved out 56 ounces of water, or .001656 cubic meters. The average dropsize, assuming a general size Seattle-area rain of 1.3 mm in diameter has a volume of 1.15x10-9 cubic meters. (Or spelled out: .00000000115).

Divide the two out and you get enough water for roughly 1.44 million raindrops!

Now, let's assume that all that water spontaneously evaporated (it won't; it'd take weeks) and for simplicity's sake, ignore any kind of wind currents that would carry the water vapor far away from here, and we'll ignore dozens of other things that would probably happen to the vapor in between and just say the water went straight from the bathtub right to a cloud over Seattle.

How much more rain would it add?

Of course, clouds are of all shapes and sizes, but let's pick a rainy cloud that is 1 mile across and 1 mile tall and is shaped more or less like a cylinder and is going to drop 0.25" of rain. How many like-minded raindrops would be in that cloud? With a little help from USAToday's "Ask Jack" column and adjusting their numbers to our much smaller cloud, our Seattle cloud that size would produce about 11.1 trillion raindrops.

(11,182,336,182,336 to be exact!)

If we're adding in our 1.44 million raindrops, that's like adding 0.000013 percent, or about 1/7-millionth of an increase.

In other words, not making much of a dent!  It's like adding one person to the population of the state of Washington.

So, as expected, the rain this week is the work of Mother Nature...and considerably larger versions of the water cycle.

(And kids, you're off the hook!)

Special thanks to Rob Wood, Neal Johnson, Nick Bond and Clint Bowman for help with the ultra complicated equations :)