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ANSWERED on Wed 27 Jan 2010 - 2:03 am UTC by byrd

Question: How many raindrops in a thunderstorm?

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 26 Jan 2010 14:12 UTCTue 26 Jan 2010 - 2:12 pm UTC 

How many raindrops are there in a storm, thunderstorm, or best of all, a hurricane?

The particular duration, location, size, wind speed, do not matter -- I can use a number for any particular kind of storm -- as long as the answer specifies these qualities.

For example: for a 10 minute thunderstorm of radius one mile in the midwest, it was calculated that there were 10 million raindrops.

Should have some academic or serious citation, rather than someone estimating in a blog (unless said estimate involves serious consideration of relevant academic works).





 27 Jan 2010 02:03 UTCWed 27 Jan 2010 - 2:03 am UTC 

Hi cyeauxg

The USA today weather resource page gives an estimated number of raindrops for an average thunderstorm as "around 1,620 trillion."

In arriving at this number they used some simple calculations and relied on some basic assumptions, based in part on information from the National Severe Storms Laboratory. Links for both are below.

Your question is similar to one asked a few years ago on Google Answers, which was how many raindrops would occupy 1 cubic foot during a thunderstorm as opposed to a light rain.

Using the answer generated there, i.e."412,700,000 little drops," you can figure the total drops for a given column in a storm. Say a storm was 15 miles wide as in the USA Today example, and 5 miles high (thunderstorms can actually reach up into the stratosphere as much as 8 miles high). The total volume would be approximately 390,180,049,332,480 cu. ft. Times 412,700,000 drops per cu. ft. that would equal 1.61027306 × 10^23 raindrops in the storm. 

Now math is not my strong suit, so you might want to recheck these numbers. I used an online caclulator to do the figuring. Here's the one I used to figure the volume in case you might like to have it too: http://www.referencedesigner.com/calc/cal_07.php

For the total drops I just used Google calculator to multiply the total cubic feet by the number of drops in one cubic foot. You type the formula into the search box, click "Search" and it figures it for you.

If you would like to do some other calculations on your own, there are several different formulas given in a "WeatherBug" high school math lesson that you might find useful. Basically it says that the number of raindrops in a given storm can be estimated by dividing the total volume of a given column of accumulated water by the volume of a single rain drop.

Since there is so much variability in both size of storms and size of raindrops, the lesson makes some assumptions such as that rainfall is occurring over a flat surface and is uniform throughout. (Note that if your version of Word doesn't have the right version of Equation Editor, the equations in the doc may show up as either empty boxes or as an error message. To see the equations, right click on the box, select "Equation Object" and "Open.")
http://weather.weatherbug.com/weatherbugachieve/lp/connections_sept06/Learning_about_flooding.doc (Scroll down to Activity 2)

I hope this information is what you were looking for. If not or you need additional assistance please Request a Clarification.




This question is actually quite complex as you likely already know. The number of raindrops in a given storm varies considerably, depending on a number of factors including the size of the drops, their density, uniformity of distribution, and velocity of fall. In case you'd like to explore the topic further, I've included a few links to some other resources that might prove interesting.

"For Hurricanes, Storms, Raindrop Size Makes All the Difference"

"The Concept of “Normalized” Distribution to Describe Raindrop Spectra: A Tool for Cloud Physics and Cloud Remote Sensing"
"... Normalizing raindrop spectra is the only way to identify the shape of the distribution."

"...for rains of a given intensity, there is a definite distribution curve of number of raindrops of a particular range of diameter."

Scroll down to the question: "Can you give a simple example of an improvement offered by polarimetric radar?"

Physics Forum: discussion on "how many drops are in 1 inch of rain on a 1 inch dia tube?"

Profiler Retrieved Raindrop Size Distributions
4.0 Jostt-Waldvogel Disdrometer




 27 Jan 2010 06:33 UTCWed 27 Jan 2010 - 6:33 am UTC 

A heavy storm provides about an inch per hour of rain, so the cubic
foot is about 12 hours' worth of heavy downpour.

http://www.flashpapers.com Term Paper




 27 Jan 2010 10:21 UTCWed 27 Jan 2010 - 10:21 am UTC 

Maybe this adds something:





 27 Jan 2010 14:32 UTCWed 27 Jan 2010 - 2:32 pm UTC 

Thanks so much! Exactly the kind of information and references I was looking for! Your time and effort is much appreciated!




 27 Jan 2010 17:20 UTCWed 27 Jan 2010 - 5:20 pm UTC 

Hi cyeauxg,

You're welcome. I'm so glad you were pleased. And thank you very much for the kind words and tip!

Best wishes,





 29 Jan 2010 16:10 UTCFri 29 Jan 2010 - 4:10 pm UTC 

Thanks for thinking of Richard-GA at Google Answers!

//the same Richard here at Uclue.com




 29 Jan 2010 17:15 UTCFri 29 Jan 2010 - 5:15 pm UTC 

You're welcome, Richard. I should have mentioned that when I posted the link! Mea culpa. Thanks for the great info!  ~Byrd (formerly Byrd-ga)




 9 Jun 2010 20:03 UTCWed 9 Jun 2010 - 8:03 pm UTC 

I was thinking about your question - - the question you originally

Say there are 180,000,000 drops in that cube, and even in a torrential
rain it takes 10 hours to fill the cube.
Ten hours is 60 x 60 x 10 = 36,000 seconds
So the drops are entering the cube at 180,000,000/36,000 = 5,000 drops
per second.
And the speed of the falling drops (terminal velocity) is maybe 100
feet per second (about 60 miles per hour), so in that one second you
can picture a column of rain that's 100 feet or 100 boxes high.
That means that there's a cubic foot of torential rain is 1/100th of
the 5,000 drops or 50 drops in a cube of torrential rain as it falls.
And normally, if either the drops are larger or it's not raining so
heavily, the real number number is probably more like 5 drops in the
falling box of rain--less than I'd have guessed but probably closer to
what you see--think how when it starts to rain it takes a while for
the splattering drops to wet the surface they're falling on.  Five
drops in 1/100th of a second is 500 drops in a second falling on a one
square foot surface.  Sounds right to me!




 9 Jun 2010 22:04 UTCWed 9 Jun 2010 - 10:04 pm UTC 

This question popped up at an appropriate time, since I am enjoying a monsoon quality thunderstorm, one with large and small drops, many more of the latter.

There is a "standard drop" for liquids, a "minim", 17 to a cubic centimeter (probably medicine dropper size); 17,000 to a liter (cube 10 x 10 x 10 cm); x 28.317 liters to a cubic ft. = a mere 481,389 drops.

Forgetting the records here:

and using the 7.5 cm/hr (3 in/hr) for an Indian monsoon, and referring to the original question:  10 minutes for a storm with a 1 mile radius (= 87.5825 million sq ft):
In ten minutes, the storm would have covered the area 1/2 inch deep, 1/24 of a cubic ft, so we divide the overall area by 24  =  3,649,271 cu. ft x 481,389 = 1,756,718,890,000 (standard "minim") drops.

Of course, this is for only ten minutes of a very localized storm with standard drops, which from my storm seems a fair average. 
But if you insist that raindrops in a thunderstorm are much larger, you will have to settle for few drops.


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