What is weather?

Weather describes the condition of the atmosphere over a short period of time e.g. from day to day or week to week, while climate describes average conditions over a longer period of time. Step outside and you experience many facets of weather. Humidity, air temperature and pressure, wind speed and direction, cloud cover and type, and the amount and form of precipitation are all atmospheric characteristics of the momentary conditions we call weather.

The sun is ultimately responsible for the weather. Its rays are absorbed differently by land and water surfaces (equal amounts of solar radiation heat the ground more quickly than they do water). Differential warming, in turn, causes variations in the temperature and pressure of overlying air masses.

As an air mass warms, it becomes lighter and rises higher into the atmosphere. As an air mass cools, it becomes heavier and sinks. Pressure differences between masses of air generate winds, which tend to blow from high-pressure areas to areas of low pressure. Fast-moving, upper atmosphere winds known as jet streams help move weather systems around the world.

Large weather systems called cyclones rotate counterclockwise in the Northern Hemisphere (clockwise in the Southern Hemisphere); they are also called “lows,” because their centers are low-pressure areas. Clouds and precipitation are usually associated with these systems. Anticyclones, or “highs,” rotate in the opposite direction and are high-pressure areas – usually bringing clearer skies and more settled weather.

The Climate System

The Climate System

The boundary between two air masses is called a weather front. Here, wind, temperature, and humidity change abruptly, producing atmospheric instability. When things get “out of balance” in the atmosphere, storms develop, bringing rain or snow and sometimes thunder and lightning too.

The weather you experience is influenced by many factors, including your location’s latitude, elevation, and proximity to water bodies. Even the degree of urban development, which creates “heat islands,” and the amount of snow cover, which chills an overlying air mass, play important roles.

The next time you watch a weather report on television, think about the many factors that influence our weather, some thousands of miles away, that help make the weather what it is.

What is Climate?

It has been said that “climate is what you expect; weather is what you get”. In other words, you can expect snow in Russia in January, but you may or may not get it on a particular day.

The climate of an area or country is known through the average weather over a long period of time. If an area has more dry days throughout the year than wet days, it would be described as a dry climate; a place which has more cold days than hot days would make it known to have a cold climate.