Weather forecasting is the application of science and technology to predict the state of the atmosphere for a given location.
Human beings have attempted to predict the weather informally for millennia, and formally since the nineteenth century.
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy.
A millennium is a period equal to 1000 years, also called kiloyears.
Weather forecasts are made by collecting quantitative data about the current state of the atmosphere at a given place and using scientific understanding of atmospheric processes to project how the atmosphere will change.
Data is a set of values of qualitative or quantitative variables.
Once an all-human endeavor based mainly upon changes in barometric pressure, current weather conditions, and sky condition, weather forecasting now relies on computer-based models that take many atmospheric factors into account.
A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically.
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.
Human input is still required to pick the best possible forecast model to base the forecast upon, which involves pattern recognition skills, teleconnections, knowledge of model performance, and knowledge of model biases.
Bias is an inclination or outlook to present or hold a partial perspective, often accompanied by a refusal to consider the possible merits of alternative points of view.
Teleconnection in atmospheric science refers to climate anomalies being related to each other at large distances.
The inaccuracy of forecasting is due to the chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, the error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes.
Hence, forecasts become less accurate as the difference between current time and the time for which the forecast is being made increases.
The use of ensembles and model consensus help narrow the error and pick the most likely outcome.
There are a variety of end uses to weather forecasts.
Weather warnings are important forecasts because they are used to protect life and property.
Forecasts based on temperature and precipitation are important to agriculture, and therefore to traders within commodity markets.
Agriculture is the cultivation of animals, plants and fungi for food, fiber, biofuel, medicinal plants and other products used to sustain and enhance human life.
Temperature forecasts are used by utility companies to estimate demand over coming days.
On an everyday basis, people use weather forecasts to determine what to wear on a given day.
Since outdoor activities are severely curtailed by heavy rain, snow and wind chill, forecasts can be used to plan activities around these events, and to plan ahead and survive them.
Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity.
Wind-chill or windchill, is the perceived decrease in air temperature felt by the body on exposed skin due to the flow of air.
In 2014, the US spent $5.1 billion on weather forecasting.