Major wind and pressure systems and related weather

Region Name Pressure Surface Winds Weather

Weather, seen from an anthropological perspective, is something all humans in the world constantly experience through their senses, at least while being outside. There are socially and scientifically constructed understandings of what weather is, what makes it change, the effect it has on humans in different situations, etc. Therefore, weather is something people often communicate about.

Effects on populations
New Orleans, Louisiana, after being struck by Hurricane Katrina. Katrina was a Category 3 hurricane when it struck although it had been a category 5 hurricane in the Gulf of Mexico.
Forecasting
Forecast of surface pressures five days into the future for the north Pacific, North America, and north Atlantic Ocean as on 9 June 2008
Once an all-human endeavor based mainly upon changes in barometric pressure, current weather conditions, and sky condition,forecast models are now used to determine future conditions. 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. The chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes mean that forecasts become less accurate as the difference in current time and the time for which the forecast is being made (the range of the forecast) increases. The use of ensembles and model consensus helps to narrow the error and pick the most likely outcome.

There are a variety of end users 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 commodity traders within stock markets. 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 the wind chill, forecasts can be used to plan activities around these events, and to plan ahead and survive them.

Equator (0°) Doldrums (ITCZ) (equatorial low) Low Light, variable winds Cloudiness, abundant precipitation in all seasons; breeding ground for hurricanes. Relatively low sea-surface salinity because of high rainfall relative to evaporation
0°–30°N and S Trade winds (easterlies) - Northeast in Northern Hemisphere; Southeast in Southern Hemisphere Summer wet, winter dry; pathway for tropical disturbances
30°N and S Horse latitudes High Light, variable winds Little cloudiness; dry in all seasons. Relatively high sea-surface salinity because of high evaporation relative to precipitation
30°–60°N and S Prevailing Westerlies - Southwest in Northern Hemisphere; Northwest in Southern Hemisphere Winter wet, summer dry; pathway for subtropical high and low pressure
60°N and S Polar front Low Variable Stormy, cloudy weather zone; ample precipitation in all seasons
60°–90°N and S Polar easterlies - Northeast in Northern Hemisphere; Southeast in Southern Hemisphere Cold polar air with very low temperatures
90°N and S Poles High Southerly in Northern Hemisphere; Northerly in Southern Hemisphere Cold, dry air; sparse precipitation in all seasons

Weather has played a large and sometimes direct part in human history. Aside from climatic changes that have caused the gradual drift of populations (for example the desertification of the Middle East, and the formation of land bridges during glacial periods), extreme weather events have caused smaller scale population movements and intruded directly in historical events. One such event is the saving of Japan from invasion by the Mongol fleet of Kublai Khan by the Kamikaze winds in 1281. French claims to Florida came to an end in 1565 when a hurricane destroyed the French fleet, allowing Spain to conquer Fort Caroline. More recently, Hurricane Katrina redistributed over one million people from the central Gulf coast elsewhere across the United States, becoming the largest diaspora in the history of the United States.
The Little Ice Age caused crop failures and famines in Europe. The 1690s saw the worst famine in France since the Middle Ages. Finland suffered a severe famine in 1696–1697, during which about one-third of the Finnish population died.

Main article: Weather forecasting
Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Human beings have attempted to predict the weather informally for millennia, and formally since at least the nineteenth century.Weather forecasts are made by collecting quantitative data about the current state of the atmosphere and using scientific understanding of atmospheric processes to project how the atmosphere will evolve.