The cartoon depicts the severe drought conditions of the summer of 1999. Soon after this cartoon appeared tropical storm Floyd dropped record rainfall over most of New Jersey.

Weather is more immediate. Is it raining now? Will it rain tomorrow? What is the expected weather for the next 5 days? Weather and the water cycle is investigated in Grade 7.

Evaporation

Heat causes water molecules to become more active. The water molecules pull away from each other as vapor and spread out filling spaces in warm air. This may cause humidity to rise. The water molecules move upward until they hit cooler air.

Condensation

Clouds form when water molecules cool and come together in the atmosphere.

Precipitation

When enough water molecules come together they become heavy and fall as precipitation. Precipitation can be in many forms including liquid (rain) or solid (snow) depending on the temperature.

Transpiration

An important source of water in the air is transpiration. Plants release water through openings in the leaves called stomata. The release of water from plants in the tropical rain forest is responsible for daily rainfall in the forest. Rain forests make their own rain!

Although low pressure is associated with foul weather and high pressure is associated with fair weather, pressure is not the cause of the precipitation. The collision of warm and cold fronts leads to precipitation. As air warms up it rises. Warm air is able to hold more water than colder air. As the air rises it cools. Water condenses out of the air. Water droplets cling to dust particles forming clouds. Storms occur when light warm air moves rapidly over cold dense air. A cold front triggers storms. Wind is the result of differences in air pressure. Air moves from high pressure to low pressure. The pressure differences are caused by uneven heating of Earth's atmosphere and surfaces. Heat radiates from the sun in the form of electromagnetic waves. It is absorbed by surfaces such as vegetation, water, and soil. The thermal energy is tranferred from the surfaces to air by conduction. The movement of air from high temperature to low temperature is an example of convection. Convection currents can cause thermals. Convection also explains local areas of high and low pressure. Sea breezes and land breezes are caused by difference in air pressure resulting from areas of uneven heating.