Severe Weather

How is the Earth heated? Solar energy heats the atmosphere, the water and the land through radiation. Heat is distributed throughout the atmosphere and the oceans through the process of convection. Thermal heat is absorbed by the atmosphere from the ground through conduction.

How Air Moves Differences in air pressure are caused by unequal heating of Earth’s surface. The region along the equator receives more solar energy , so the heated equatorial air rises and creates a low-pressure center. Conversely, cold air near the poles sinks and creates high-pressure centers. Differences in air pressure at different locations on Earth create wind patterns. .

Air moves from areas of high pressure to areas of low pressure There is a general, worldwide movement of surface air from the poles toward the equator. At high altitudes movement of air from the equator to the poles.

When pressure differences are small, air remains stationary A large body of air throughout which temperature and moisture are similar is called an air mass Polar air masses are cold and dry Tropical air masses are warm and moist The process by which the temperature of a mass of air decreases as the air rises and expands is called adiabatic cooling

For a FRONT to form, one type of air mass must collide with a different type of air mass Stationary Front- When 2 air masses move parallel to one another and neither air mass is displaced. Occluded Front- When a cold air mass overtakes a warm air mass off the ground and over another air mass.

Cold Front Forms when a cold air mass overtakes a warm air mass Moving cold air lifts the warm air If the air is moist, clouds form For clouds to form, particles in the atmosphere called CONDENSATION NUCLEI must be present so the water vapor has a surface in order for condensation to take place.

Cumulonimbus clouds typically form along fast moving cold fronts, and often bring thunderstorms. A SQUALL LINE ( a long line of heavy thunderstorms ) may occur in the warm moist air ahead of a fast moving cold front. A slow moving cold front slowly lifts the moist air and produces weak storms and light precipitation.

Warm Fronts When a warm air mass overtakes a cold air mass Generally produces precipitation over a large area and sometimes violent storms. A DRY LINE is the boundary separating moist and dry air masses

Thunderstorms Cumulonimbus clouds often bring thunderstorms. A thunderstorm is a usually brief, heavy storm with rain, wind, lightning and thunder Lightning- Forms when clouds discharge electricity Thunder- A loud noise produced when released electricity heats the air and the air expands rapidly.

Hurricanes A severe storm that develops over tropical oceans, whose strong winds (120 km/h +) spiral in toward the intense low-pressure center.

Tornados A destructive, rotating, funnel shaped column of air with high wind speeds The smallest, most violent, and shortest lived storms Winds may reach more than 400 km/h

FLOOD A flood is an overflowing of a large amount of water beyond its normal confines. A flash flood is a rapid rise of water along a stream or low lying urban area. Caused by heavy rain, dam break, levee failure, rapid snowmelt or ice jams.

Major Flash flood disasters

DROUGHT A drought is a period of unusually persistant dry weather that persists long enough to cause serious problems such as crop damage and/or water supply shortages. The severity of the drought depends upon the degree of moisture deficiency, the duration, and the size and location of the affected area.

MITIGATION The act of reducing the severity and seriousness of a severe weather event. Scientists use Doppler radar to warn people of approaching storms. Examples: Soil conservation is an indirect method of flood control; dams, artificial levees, and overflow channels are direct methods of flood control.