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Forecasting the weather Weather: The state of the atmosphere at a specific time and place. Meteorologist: scientists who study the atmosphere Weather forecasts are issued: – to save lives – reduce property damage – reduce crop damage – to let the general public know what to expect How far ahead can meteorologists accurately predict the weather? • 0-12 hrs: pretty accurate except for unpredictable local storms. • 12-48 hrs: are able to predict which areas will be hit by severe storms. • 3-5 days: big events or storms can be predicted (hurricanes, floods). • 6-10 days: can give an average temp for a period of time. How do they do it? • Meteorologists look at: – Existing weather conditions over a large area. – Current data gathered from: • Satellite images • Weather stations • Weather balloons – This data includes: • • • • Three important factors that shape the weather in a given region are: — temperature Atmospheric pressure — pressure Wind direction and speed — water Temperature of the air Humidity, clouds, and precipitation Making a weather map • The basic tool of a weather forecaster is the WEATHER MAP. • The weather map shows the: – distribution patterns of atmospheric pressure – wind – temperature and humidity at the different levels of the atmosphere. Low and High Pressure Systems • When a cold front moves into a region and warm air is forced upward, an area of low pressure is created near Earth’s surface. • A center of high pressure tends to be found where a stable cold air mass has settled in a region. Remember: Wind is a horizontal movement of air from a area of high pressure to an area of low pressure. Isobars • Curved lines that indicate areas of equal air pressure. • Indicate wind speed and wind direction Iso = equal bar = pressure Closely spaced lines= high change in pressure + high wind speed. Widely spaced lines= slow change in pressure + low wind speed. High pressure system (depicted by an "H") Low pressure system (depicted by an "L” Wind • Winds are identified as the direction FROM which they come. From which direction is the wind coming according to this wind feather? Weather Symbols fog haze , rain snow * slight rain thunderstorm drizzle lightning showers . ice or snow pellets cloud development not observed no clouds about 60% about 10% about 75% about 25% about 80% about 40% completely overcast about 50% sky obscured