Thunderstorm: a convective rain or snow shower accompanied by thunder and lightning. At any moment, there are up to 1800 T-Storms in progress around the world. In the US, T-storms provide a large amount of the rainfall needed for agriculture (especially in the central Plains).

LIGHTNING

Precipitation Theory: collisions between hail/graupel (-) falling due to gravity and ice

crystals (+) rising due to updrafts, sets up an abundance of negative charge (-) at the base

of a Cb and an abundance of positive (+) charge at the top.

• The air under a Cb has areas of positive (+) ions that can be drawn into the base of the Cb via the updrafts. (The negative charge in the base of the Cb can be 10,000 time that of the normal atmospheric charge!)

• A local discharge between the "-" charge in the base of the Cb and the "rogue" area of "+" ion air results in a PILOT LEADER (which can move at a speed of 270,000 mph toward the ground!).

• The "-" charge pours into the pilot leader to create STEPPED LEADERS (about 1" in diameter), which advance earthward in a millionth of a second!

• The stepped leaders attract "+" charge from tall objects (such as antennas, trees, power lines, etc.), which sets off a spark that travels about 50 m (162 feet) to meet the stepped leader.

• A channel is established! Electrons ("-") surge to the ground and pile up in the lowest part of the channel to cause a brilliant RETURN STROKE upward from the ground to connect with the stepped leader.

• The "flicker" is caused by successive transports of electrons, by DART LEADERS (separated by 1/200th of a second) from higher parts of the Cb.

  Positive Flash: from upper portion of Cb to "-" earth ... can strike far away from the cloud itself.

  Fact: 80% of all lightning is "in-cloud" ... most of the remaining 20% is "cloud-to-ground" ... with "cloud-to-cloud" and "cloud-to-air" being rare.

THUNDER

Lightning heats air to 50,000 F (four times hotter than the surface of the sun!). The air expands explosively, producing a high pressure shock wave that propagates away from the lightning stroke as it ascends into the Cb. The sound travels at 1100 feet per second and the light at 186,000 miles per second. You can determine the approximate distance to the lightning stroke by counting the seconds from when you first see the lightning to when you hear its thunder. (Five seconds is roughly one mile away.) Thunder cannot be heard more than 15 miles away. HEAT LIGHTNING is a thunderstorm in the distance, that is too far away to hear the thunder.