High and Low Pressure Areas• High pressure • Air rises in lowcauses air to sink pressure areas and forms water• Usually results in dropletsseveral days of clearsunny skies • Usually results in rain and storms
Barometer – tool used to measure air pressure.High pressure brings mild winds, stable temperatures, and clear weather. H Low pressure brings strong winds, dropping temperatures and precipitation. L
Barometric Pressure – tells us when weather will change. when it falls - low pressure moving in Warm air= Air Pressure expanding or rising air= leaves L behind L pressure when it rises- high pressure moving in Cold Air Pressure Air=sinkingair= leaves an area of H H pressure
Global Air Masses• North America gets 5 types of air masses• Defined by areas of origination• Highly variable in terms of temperature and moisture
The Jet Stream guides the movement of different air masse s across the United States. A jet stream forms high in the upper troposphere over the boundary between two air masses of different temperature. The greater the temperature difference between the air masses, the greater the air pressure difference, and the faster the wind blows in the jet stream. This river of air has wind speeds which often exceed 100 mph, and sometimes peak over 200 mph. Jet streams usually form in the winter, when there is a greater contrast in temperature between cold continental air masses and warm oceanic air masses.
Wind is caused by air flowing from high pressure to low pressure. Sincethe Earth is rotating, however, the air does not flow directly from high to lowpressure, but it is deflected to the right (in the Northern Hemisphere; to the left inthe Southern Hemisphere), so that the wind flows around the high and lowpressure areas.The closer the high and low pressure areas are together, the stronger the"pressure gradient", and the stronger the winds. On weather maps, lines ofconstant pressure are drawn (as in the example, above) which are called"isobars". The closer these lines are together, the stronger the wind.
Air Mass a huge “bubble” of air that shares the same temperature and pressure. (can be big enough to cover several states!)Air Masses are huge clumps of air that move around the Earth, bringing changes in… weather.Air masses are like the surface they form over.
The air mass shown above formed over land in northern Canada. Therefore the air mass will be… cold and dry.
A polar air mass brings cold airCold Air Mass – this is an air mass made up of cool temperatures and high pressure. Usually does not hold much moisture Forms over cold water or land. H
The pink air mass formed over the ocean near the equator. The air mass will be… warm and moist.
Warm Air Mass – this is an air mass made up of warm air that has a low pressure. Usually holds a lot of moisture. Forms over hot land or water. L A tropical air mass brings warm air
The map symbol for a warm front is a curved line with small… rounded knobsWhen warm air catches up to a cold air mass, what is formed?... warm front
When a warm air masscatches up with a coldair mass, it forms a… warm front The warm air…slides over the top of the cold air, before … pushing it away.Weather associated with warm fronts are…. Clouds and long periods of steady rain
From the map above, you can predictthat the weather over the Great Lakes will be getting … warmer
Warm or cold front stops moving.Light wind andprecipitation mayoccur across the front boundary
• One front overtakes another • Cold front typically faster moving• Can have warm and cold occluded fronts • Creates Precipitation