1	Chapters 20-22: Hailstorms, Lightning, Downbursts
2	Hail
3	Hailstone Size
4	The Largest Hailstone ever Collected in the US
5	Hailstone
6	Hail Growth
7	Hail Curtain
8	Chapter 21 : Lightning
9	Major Sequence for Lightning Electrification of a cloud: Charge Separation Development of a path through which the electrons can flow Discharge: Lightning
10	Charge Separation in Clouds Positive charges in the upper portions of the cloud; Negatively charges in lower portions; Small packet of positive charges in the cloud base. lightning occurs only in clouds that extend above the freezing level è charge separation is related to ice crystals. Lighter crystals collide with heavy hailstones in the cloud. The lighter crystals are positively charged and move to upper portions of the cloud. The heavy hail stones are negatively charged and move to the lower portion of the cloud.
11	Creation of a Lightning Stroke
12	Charge Distribution
13	Lightning Cloud-to-Cloud Lightning 80% of all lightning Electricity discharge happens within clouds Causes the sky to light up uniformly (sheet lightning) Cloud-to-Ground Lightning 20% of all lightning Electricity discharge happens between cloud base and ground
14	Step Leaders The dry air is a good electrical insulator, so a flow of current can not occur. For cloud-to-ground lightning to occur, a stepped-leader must emanate from the cloud base. The leader is essentially an ionized particle chamber about 10 cm (4 in) in diameter which forks repeatedly from a main channel. Each section travels about 50-100 m in a microsecond (a millionth of a sec). The sections continue until contact is made with an unlike charged area (the ground).
15	Return Strokes Upon connection, electrons flow resulting in an illuminated return stroke. Although the electrical current is from the cloud to the ground (moves downward), the return stroke is in the opposite direction (move upward). The upward return stroke happens so fast, our eyes can not resolve its upward direction.
16	Dart Leader and Flash Usually more than one stroke is needed to neutralize all negative ions. Another leader, or dart leader, is initiated and a return stroke follows. Dart leader moves downward faster than step leader. The process is repeated about 2-3 times on average. Individual strokes are almost impossible to detect. We call a combination of all strokes a lightning flash.
17	Thunder
18	Chapter 22: Downbursts
19	Downburst
20	Downburst Formation
21	Structure of Downburst
22	Downburst's Threat to Aircraft