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Published byIrvin Gundry Modified over 2 years ago

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Heavy, Heavy Hangs Over Your Head – Weighing a Thunderstorm

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You can look at the weight of a thunderstorm in various ways. Well explore two of them: The weight of water falling as rain over a parcel of land of a given size. The weight of water suspended in a thunderstorm cloud.

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Suppose we have a parcel of land that is one square mile in area… To make life easier, well suppose our parcel is essentially flat and non-porous.

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Lets further suppose that enough rain has fallen on our parcel to cover it uniformly to a depth of 1 inch. So, how much does all that water weigh? (For this example well use English units of measurement rather than metric.)

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27,878,400 sq. ft. in 1 sq. mile |--------------- 5,280 feet ---------------------------------| |--------|-------- |----------------------- 5,280 feet ----------------|

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1 square foot = 12 x 12 inches = 144 square inches

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1 sq. mile So… 1 square mile = 5,280 feet X 5,280 feet = 27,878,400 square feet 1 square foot = 12 inches X 12 inches = 144 square inches 27,878,400 square feet X 144 square inches = 4,014,489,600 square inches in 1 square mile (thats 4 billion + square inches!)

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|----- 1 inch ---| So, if enough rain were to fall such that all 4,014,489,600 square inches of land surface were uniformly covered to a depth of 1 inch, that would be 4,014,489,600 cubic inches of water. How much do you suppose all that water would weigh???

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Lets look at it in a slightly different way… A cubic foot is 12 X 12 X 12 = 1,728 cubic inches, so the water standing on our parcel represents…. 4,014,489,600 cu. in. / sq. mile divided by 1,728 cu. in. / cu. ft. = 2,323,200 cubic feet of water per square mile

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1 cubic foot of water weighs 62.31 pounds approximately – depending on temperature and any contaminants, so…

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2,323,200 cubic feet of water times 62.31 pounds per cubic foot equals a whopping 144,758,592 pounds !!! Thats equivalent to about 1,800 fully loaded 18-wheelers – enough to stretch for just over 22 miles along I-81! Clearly, there is A LOT of water in a thunderstorm!!!

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As an aside, 2,323,200 cubic feet of water is equivalent to 17,377,536 gallons – there are 7.48 gallons in a cubic foot – so the amount of water covering a square mile to a depth of 1 inch would be enough to fill 68.65 Olympic sized swimming pools! (An Olympic sized pool holds about 253,125 gallons.)

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Okay, then, lets look at this another way – from the storm clouds point of view!

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This time, well use metric measurements. Lets assume that our storm cloud is pretty averagein fact, fairly small as storm clouds go. Obviously, a real cloud is irregularly shaped, but were going to think of our cloud as an oblong box. Our cloud will cover an area of 1.6 km 2 (This is a square mile, in case you were wondering but I wont use that term again!) So how tall is our cloud? Some storm clouds can reach incredible heights, but lets assume that our cloud is only 10,000 meters tall.

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So we can think of our cloud as a box with a volume of 1,600 meters X 1,600 meters X 10,000 meters. That works out to a total of 25,600,000,000 cubic meters! Scientists, of course, would prefer to state that using scientific notation. Thus it would become 2.56x10 10 m 3 Either way, were looking at over 25 billion cubic meters of volume. |---- 1600 m ----| |------------------- 10,000 m -------------------|

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So how much water can that big a cloud hold? The answer depends upon the density of the water vapor that makes up the cloud. An average storm cloud may have a density of about 10 grams per cubic meter (10 g/m 3 ) so….

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2.56x10 10 m 3 times 10 g/m 3 equals 2.56x10 11 grams of water in a thunderhead. There are 1,000 grams in a kilogram, so there are 256,000,000 kilograms of water in our storm cloud. A kilogram weighs about 2.2 pounds, so the weight of our storm cloud in pounds is about 563,200,000 pounds!

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By comparison, a fully loaded 747 weighs about 875,000 pounds. Thus, it would take 644 fully loaded 747s to equal the weight of a small thunderstorm! And all that water just floats around up there….!

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The End

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