Weather

What? And How?

1. How is lightning formed? Cumulonimbus clouds must become electrically charged therefore, in most rain clouds the bottom of the rain cloud is negatively charged and the top is positively charged. Lightning is created as a discharge of built up energy due to the separation of positive and negative charges which are generated inside the thunderstorm.

2. How are tornadoes formed? Tornadoes form in unusually violent thunderstorms when there is sufficient instability, and wind shear present in the lower atmosphere. Instability refers to warmer and more humid than usual conditions in the lower atmosphere, and possibly cooler than usual conditions in the upper atmosphere. Wind shear in this case refers to the wind direction changing, and the wind speed increasing, with height.

3. Parts of a thunderstorm
a) Updrafts/Downdrafts- Also known as rising and sinking air. All thunderstorms require instability and lift. The lift is the mechanism that releases the instability. Lift is produced by such things as fronts and low pressure troughs, or by air rising upslope.
b) Wind Shear- The difference in wind speed and direction over a relatively short distance in the atmosphere. Wind shear can be broken down into vertical and horizontal components, with horizontal wind shear seen across fronts and near the coast, and vertical shear typically near the surface, though also at higher levels in the atmosphere near upper level jets and frontal zones aloft.
c) Outflow Phenomena- Damaging thunderstorm winds.
d) Wall Clouds-A wall cloud, or pedestal cloud, is a cloud formation associated with thunderstorms. It is a marked lowering typically beneath the rain-free base portion of deep cumulous clouds, and indicates the area of primary and strongest updraft which condenses into cloud at altitudes lower than that of the ambient cloud base. Most strong tornadoes form within wall clouds.
4. Types of thunderstorms
a) Single Cell Storms- Pulse storms can produce severe weather elements such as downbursts, hail, some heavy rainfall and occasionally weak tornadoes.
b) Multicell Cluster Storms- A group of cells moving as a single unit, with each cell in a different stage of the thunderstorm life cycle. Multicell storms can produce moderate size hail, flash floods and weak tornadoes
c) Multicell Line Storms- Multicell line storms consist of a line of storms with a continuous, well developed gust front at the leading edge of the line. Also known as squall lines, these storms can produce small to moderate size hail, occasional flash floods and weak tornadoes.
d) Supercells- Defined as a thunderstorm with a rotating updraft, these storms can produce strong downbursts, large hail, occasional flash floods and weak to violent tornadoes.