(female narrator)
Winter is here.
Let it snow, let it snow,
let it--Wait.
Is that thunder?
Seasonal Science
brings you "Thundersnow."
If you happen to see
the flash of lightning
and hear thunder
during a snowstorm,
consider yourself lucky.
In the U.S., less than
ten storms per year
produce what is known as
"thundersnow."
But what causes
this crazy winter phenomenon,
and why is it so rare?
First, let's start
with your average, everyday,
not-so-special snowstorm.
A typical winter snowstorm
forms when warmer air
is lifted over colder air.
As the warm air rises,
the moisture condenses and forms
clouds and precipitation,
and due to
the cold surface temps,
snow falls to the ground.
But there's a major difference
separating ordinary snowstorms
from thunder snowstorms,
and that is the speed
at which that warm air rises.
In a thunder snowstorm,
upward moving air
rises much faster.
We're talking meters
per second
versus an ordinary snowstorm's
centimeters per second.
This rapid updraft
makes precipitation
and cloud particles collide.
The faster the updraft,
the more collisions,
and like
in a summer thunderstorm,
these collisions cause
different cloud parts
to develop positive
or negative charges.
Once the difference in charges
becomes large enough,
lightning discharges
to equalize everything.
And what happens
after lightning?
[thunderclap]
Hello, thundersnow.
Sounds simple enough, right?
But thundersnow is rare
because getting an updraft
that fast during winter
is difficult.
Cold air in winter
tends to make things stable.
Only the right circumstances can
get air to rise quick enough.
Thunder snowstorms form
when either warm water
heats the surface air,
which rises,
creating a fast updraft,
or when strong weather systems
cause air already aloft
to rise faster than normal.
Even when all the factors
are in place,
hearing the actual thunder
is not a given.
Because of all the snow
created during such storms,
the rumble of thunder
is muffled enough
that it can only be heard
within a couple miles
of the lightning source.
So, if you do happen to witness
this crazy weather phenomenon,
go ahead and celebrate.
Snow cones anyone?
[people cheering]
Accessibility provided by the
U.S. Department of Education.
