By Chris Spears

DENVER (CBS4) – Monsoon storms are known for being packed with tropical moisture and Wednesdaynight lived up to that reputation, especially in Douglas County.

Using data from the CoCoRaHS Network I’ve estimated that over 400 million gallons of water likely fell over Highlands Ranch.

Extra: Click here to view CoCoRaHS maps where you live

Below is an explanation of how I arrived at that number.

(credit: CoCoRaHS)

Using five data points that are almost equally spread out across Highlands Ranch (yellow dots on the map above) I came up with a storm average of 1.01″ of rain. (which I rounded to one inch)

I then used the following two facts and did a little math.

1″ of rain over 1 square mile = 17.38 million gallons of water (per USGS)

Highlands Ranch is listed as 24.29 square miles (according to google)

Do the math and you come up with 422,160,200 gallons of water.


The point of this story is not to nitpick the math and methodology because I know this is just a crude estimate that is using a very limited data set.

My goal here is to educate you on how such a limited supply of water vapor in the atmosphere over a very dry state like Colorado can produce such an enormous amount of water that falls from the sky.

It’s no wonder we have to worry about flash floods this time of year.

(credit: CBS4)

In reality the number of gallons that fell over Highlands Ranch is likely higher because there were pockets of more intense rain within the line of storms.

And in places closer to Castle Rock there were several CoCoRaHS stations that reported more than two inches of rain, which means there was likely over a billion gallons of water that fell from the sky in central and eastern Douglas County last night.

Meteorologist Chris Spears travels weekly in the CBS4 Mobile Weather Lab reporting about Colorado’s weather and climate. Check out his bio, connect with him on Facebook or follow him on Twitter @ChrisCBS4.


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