Weather refers to the atmospheric conditions that bring wind and precipitation to the surface of the earth. It is a global phenomenon that is mainly driven by the heat of the sun. Convection effects cause the air to rise in areas where sunlight is penetrating the atmosphere. As the air rises, it may collect water from the oceans, mainly, which is held in suspension. The air and water move in the atmosphere in the form of clouds. Often the air cools significantly as it moves. This reduces the ability of the air to retain the water. The water falls to the earth where it usually travels back to the ocean. There are many observable weather features. Some are mild while others are some of the most violent conditions observed by the earth. Weather affects many human activities from food production to travel to basic living conditions. Significant weather features include:

These are accumulations of water vapor which has been raised into the atmosphere by the heating effect of the sun. Clouds can persist at many levels from sea level to the lower atmosphere. They move in the air due to general movements of air caused by the sun.

When clouds are not able to contain their moisture, water is released to drop towards the earth. Depending on the height of the clouds and the temperature of the air, the water may fall as various categories of precipitation. Low clouds and warmer temperatures cause rain. Higher clouds release snow, rain that has frozen while high aloft. If rain falls from a cloud and freezes during the descent to the earth, hail results. Depending on the amount of precipitation, there can be noticeable effects on the earth. Rain can result in flooding. Snow can accumulate causing travel difficulties and damage to weaker structures. Hail can be extremely violent due to the mass of ice. Some hail falls as stones ranging in size from pea sized or smaller, up to large pieces that weigh more than a pound each. These heavy hail stones are extremely dangerous.

When an amount of air is heated by the sun, it rises. As it cools, it descends until it contacts the surface of the earth. This movement of air is termed wind. Air, or wind, is capable of moving at speeds ranging from barely detectable to more than 100 miles per hour. The Beaufort Scale was established to rate the speeds and give them official names. It is based on the observed effects that the wind has such as moving light material such as smoke or dust up to the widespread destruction of trees by wind.

This is among the mildest form of weather. It refers to very light wind that is barely perceptible by people. Breezes are usually very easy to tolerate. They can lead to more severe weather conditions, however. The breeze term describes wind conditions that are barely felt up to a strong breeze which has be the ability to generate fairly large waves on the water and blow over empty garbage cans on land.

Gale Wind
Stronger than a mere breeze, a gale is a rather more significant weather situation. There is a range of gale severity. A moderate gale can cause ocean waves to break and spray water along the wind direction. Trees are in motion and may experience some damage to weak branches. Fresh gales are stronger while strong gales have very noticeable effects. These are marked by winds of about 50 miles per hour. Waves are high with crests that break and spray a lot of water and foam in the wind direction. Navigation is a serious concern for boats and many ships will take extensive safety precautions. The strong gale has the ability to break branches from trees and even topple weaker ones. Various items on land may be toppled.

When winds exceed 55 miles per hour, a storm is declared. A violent storm will have wind speeds up to 72 miles per hour. Waves during storms can be exceptionally large, up to 50 feet at the crest. Ships take extreme precautions to avoid travel during storms. Large patches of wind generated foam cover much of the water surface. There is widespread destruction of vegetation. Certain building structures may have roofing partially torn away. Travel by automobile or on foot will be difficult and possibly dangerous.

When the wind speed exceeds 73 miles per hour, a hurricane is declared. This is an extremely violent and dangerous weather event. The sea is completely covered with foam and spray from waves exceeding 50 feet at times. There is severe destruction on land throughout the path of a hurricane. Vegetation is destroyed, buildings can be damaged, sheds and mobile homes may be destroyed. Debris can be hurled about. Travel by any means is extremely difficult and dangerous. Hurricanes have a distinct center, around which the winds rotate at great speeds. Each is a defined event of such significant concern that they are given names from a registry. This allows quick communications to warn people about impending hurricanes and to describe the effects in relation to the particular hurricane. Some devastating hurricanes in history have been named Hazel, Andrew and Katrina. Katrina was an extremely damaging hurricane that resulted in over 1800 deaths and total property damage valued at $81 billion dollars in 2005. It was particularly devastating to the city of New Orleans which was still repairing the damage 5 years later.

Perhaps the strongest and most dangerous weather condition is the tornado. While hurricanes are the most powerful weather force as they have extreme winds that affect thousands of square miles during each one, a tornado is a very concentrated event that brings winds of between 110 and 300 miles per hour to a very small point at the earth's surface. The extreme focus of such strong winds causes havoc to ground structures and vegetation. The largest tornado can be about 2 miles across and travel for dozens of miles, destroying most everything on their path. They are formed when violent air masses, such as storms, combine resulting in a tremendous concentration of wind. While a tornado can form nearly anywhere, they are much more common where very hot air masses are combined with cold air masses. This is experienced most often in Tornado Alley, a large area located through the central United States.