One English saying that has always puzzled the general public
about the weather is the title of today's weatherwise
discussion. Has it ever rained cats and dogs?
This question can be answered by looking at the dynamics of
some severe local storms such as tornadoes. These storms,
which can be likened a whirlwind imbedded in the rain
contain so much energy in them to lift heavy objects. The
energy derives from the fact that within the storm there is
great atmospheric pressure differential, which is translated
into rotational motion. There is low pressure inside a
tornado and high pressure exists outside. As a result the
tornado acts as a vacuum cleaner. As it travels it sucks up
into the storm debris and any other objects around. As the
debris rises up into the storm they reach an area where
there is an outflow and hence they have to be thrown out of
the storm. So they come down raining (literally).
It is actually on record that in some countries such storms
have sucked in domestic animals such as cats and dogs, which
have come raining elsewhere as the storm moves.
Here in Malawi there have been incidents where similar
storms on the lake have sucked in fish, which have later
rained on land. So it actually can rain cats and dogs.