Heavy, Heavy Hangs Over Your
Head – Weighing a
Thunderstorm
You can look at the “weight” of a
thunderstorm in various ways. We’ll
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.
Suppose we have a
parcel of land that is
one square mile in
area…
To make life easier, we’ll
suppose our parcel is
essentially flat and
non-porous.
Let’s 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 we’ll
use English units of
measurement rather
than metric.)
|--------------- 5,280 feet ---------------------------------|
|----------------------- 5,280 feet ----------------|
|
-
27,878,400 sq. ft. in 1 sq. mile
1 square foot = 12 x 12 inches =
144 square inches
So…
1 square mile = 5,280 feet X 5,280
feet = 27,878,400 square feet
1 sq. mile
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
(that’s 4 billion + square inches!)
|----- 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???
Let’s 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
1 cubic foot of water weighs 62.31 pounds
approximately – depending on temperature and any
contaminants, so…
2,323,200 cubic feet of water times 62.31 pounds per cubic foot
equals a whopping 144,758,592
pounds!!!
That’s 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!!!
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.)
Okay, then, let’s look at this another way – from the storm cloud’s point of view!
This time, we’ll use metric measurements.
Let’s assume that our storm cloud is pretty
average—in fact, fairly small as storm clouds
go. Obviously, a real cloud is irregularly
shaped, but we’re going to think of our cloud as
an oblong box.
Our cloud will cover an area of 1.6 km2 (This is
a square mile, in case you were wondering—
but I won’t use that term again!)
So how tall is our cloud? Some storm clouds
can reach incredible heights, but let’s assume
that our cloud is only 10,000 meters tall.
|------------------- 10,000 m -------------------|
|---- 1600 m ----|
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 2.56x1010 m3
Either way, we’re looking at over 25 billion
cubic meters of volume.
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/m3) so….
2.56x1010 m3 times 10 g/m3 equals
2.56x1011 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!
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….!
The End