Weather Notes:



|term |definition or information |diagram or picture |

|precipitation |rain, sleet, hail, snow |rain gauge |

| |type of precipitation determined largely by air temp | |

|anemometer |used to measure wind speed |anemometer [pic] |

| |miles per hour (mph) | |

|wind vanes |Used to measure wind direction |wind vane |

|air pressure |barometric pressure (millibars) |barometer |

| |weight of air pressing at a given location | |

| |varies mostly due to the sun heats Earth’s surface unevenly | |

| |****changes in air pressure are a sign that weather is about to change (drops rapidly | |

| |means a low pressure system is approaching) | |

| |Air over a heated surface absorbs heat from the surface, expands, and becomes less dense. | |

| |As the air’s density decreases, air pressure also decreases. | |

| |**With hurricanes, an increase in air pressure causes the hurricane’s wind speed to | |

| |decrease (weakens). When the pressure decreases (lowers), the hurricane’s wind speed | |

| |increases (intensifies). |[pic] |

| |Tornado----air pressure drops quickly; wind blowing in opposite directions | |

| |Low-pressure system--- | |

| |---usually bring cloudy, rainy, or snowy weather | |

| |---develops when an air mass at the Earth’s surface rises | |

| |(vacuum cleaner) | |

| |High-pressure system--- | |

| |---sunny, fair weather, clear skies, calm conditions | |

| |---develops when an air mass sinks toward the ground | |

| |(hair dryer) | |

|temperature |determines how much water vapor the air can hold |Fahrenheit or Celsius thermometers |

| |Warm air can hold more water vapor than cold air. |[pic] |

| |Water evaporates faster at higher temperatures. | |

| |On hot days more water evaporates and stays in the air. | |

| |As warm, wet air cools, the water vapor may condense, form clouds, and fall as rain. | |

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|humidity |amount of water vapor in the air (damp/sticky) |psychrometer |

| |Relative humidity--- compares the amount of water vapor in the air (absolute humidity) to |[pic] |

| |the amount of water vapor that air can hold at a given temperature. |hygrometer |

| |--- given as a percentage % |[pic] |

| |--- measured using hygrometers | |

| |--- one common type is the psychrometer which | |

| |consists of two thermometers | |

| |---affects the dew point | |

| |Dew---water vapor that condenses on a surface | |

| |---Dew formation depends on the air temperature and the amount of water vapor in the air. | |

| |---The dew point is a measure of the temperature at which more water vapor will condense | |

| |onto a surface than will evaporate from it. | |

|air mass |a large volume of air with about the same temperature, air pressure, and humidity | |

| |throughout | |

|front |a boundary between two air masses | |

| |High-pressure systems move into low-pressure systems at fronts. | |

| |most changes in weather occur at fronts | |

|cold front |cold air mass pushes under a warm air mass, forcing the warm air to rise sharply |[pic] |

| |Because the air rises quickly, tall clouds often form. | |

| |Heavy rain, thunderstorms, and snowstorms occur at cold fronts. | |

| |When the cold front passes, the temperature drops and the weather clears. | |

|warm front |warm, moist air mass slides up and over a cold air mass |[pic] |

| |Since moist air is rising at a warm front, clouds usually form. | |

| |Warm fronts usually bring light rain and cloudy weather. | |

| |After a warm front passes, the temperature rises and the weather clears. | |

|stationary front |two air masses meet and stop moving |[pic] |

| |neither has enough force to lift the warm air mass over the cold air mass | |

| |brings light winds and wet weather, which can last for several days | |

|occluded front |forms when a warm air mass is caught between two colder air masses, one of which overtakes|[pic] |

| |the other | |

| |The warm air is forced to rise. | |

| |if an occluded front is accompanied by strong winds and cooler temperatures, it can bring | |

| |heavy rain or snow | |

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|hurricane--- |large, rotating low-pressure system that forms over warm tropical water | |

|Gulf of Mexico, |wind speeds of at least 74 mph (category 1) |[pic] |

|Atlantic, Caribbean, |rotate counterclockwise | |

|Eastern Pacific Ocean |As long as a hurricane is over warm water, moist air rises into it and gives it energy. |[pic] |

|typhoons--Northwest |can cause severe damage | |

|Pacific Ocean |use satellite photos to show the size and location | |

| |Prediction cones---Scientists also use data from past hurricanes to develop computer | |

|tropical cyclones--- |models that predict how a new hurricane may behave. These predictions can save lives by | |

|Australia and Indian |warning people to move out of a hurricane’s path. | |

|Ocean |**With hurricanes, an increase in air pressure causes the hurricane’s wind speed to | |

| |decrease (weaken). When the pressure decreases (lowers), the hurricane’s wind speed | |

| |increases (intensifies). | |

|Weather Data Technology-- |

|weather satellites |orbit Earth |[pic] |

| |providing images of the movement of clouds, storms, | |

| |water vapor, air masses | |

|Doppler radar |radio/microwave |[pic] |

| |located on Earth’s surface gather data by sending out | |

| |radio signals that are reflected off objects such as | |

| |raindrops, snowflakes, hailstones, or clouds | |

| |detects the type and amount of precipitation, location, | |

| |height, and movement of clouds | |

|government agencies |NOAA ---National Oceanic and Atmospheric Association |[pic] |

| |NWS--- National Weather Service | |

|Climate Zones--- temperature and precipitation are key factors |

|tropical zone |closest to equator | |

| |tend to be warm to hot year-round | |

| |receive direct sunlight throughout year | |

|polar zones |farthest from equator | |

| |near Earth’s North and South Poles | |

| |least direct sunlight throughout year | |

| |tend to be cool to cold year-round | |

|temperate zones |located between polar and tropical | |

| |angle at which the sun’s rays strike these regions | |

| |changes greatly throughout the year | |

| |distinct seasons with very different temperatures | |

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|convection current |circular flow of gas or liquid caused by | |

| |temperature differences | |

| |heat moves warmer to cooler | |

| |continuous movement of rising warm air and sinking | |

| |cool air | |

| |sun sets currents in motion by heating Earth’s | |

| |surface unevenly (more heat near equator) | |

| |When air gets warmer, the molecules move faster and| |

| |spread farther apart. | |

| |causes sea and land breezes | |

| |Higher, cooler air sinks since it is denser than | |

| |warm air | |

| |After it sinks, the cooler air is warmed by the hot| |

| |sand, becomes less dense and rises. | |

|Global winds--- by the heating of the sun and spinning of Earth; steers weather; solar energy absorbed near equator warms air forming large areas of low pressure; |

|warm air rises as the colder air near the poles sinks forming high pressure areas |

|polar easterlies |cold, dense air moves away from the high pressure areas |[pic] |

| |around the poles and curves west | |

| |extend from the poles to 60° latitude. | |

| |In the Northern Hemisphere, the polar easterlies bring cold| |

| |arctic air down over the United States. This arctic air | |

| |brings snow and freezing weather. | |

|trade winds |warm, rising air at the equator moves away from the equator| |

| |Winds that blow toward the equator from 30° latitude | |

| |Cooler air north and south of the equator moves toward the | |

| |low pressure area at the equator. This cooler air makes up | |

| |the trade winds. | |

| |Coriolis effect causes these winds to curve. | |

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|westerlies |winds that flow from west to east and toward the poles | |

| |between the polar easterlies and the trade winds | |

| |found between latitudes of 30° and 60° | |

| |The westerly wind belt carries storms across the United | |

| |States. | |

|doldrums |located at equator | |

| |little to no wind | |

|Coriolis effect |paths of winds and ocean currents curve due to Earth’s |[pic] |

| |rotation | |

| |rotation or spinning of Earth on its axis plays a role in | |

| |wind patterns | |

| |weather tends to move in curving, circular patterns | |

| |In the Northern Hemisphere, winds moving north curve to the| |

| |east and winds moving south curve to the west. | |

| |Weather forecasters need to know this to predict where | |

| |winds and air masses are likely to go. | |

| |At every 30° latitude, the Coriolis effect causes winds to | |

| |curve in a different direction. | |

|jet streams |high in the atmosphere, flowing from thousands of |[pic] |

| |kilometers from west to east | |

| |do not follow regular paths | |

| |around Earth | |

| |move north and south over | |

| |time | |

|Gulf Stream |Gulf Stream’s warm sea surface temps aid in the formation |[pic] |

| |and strengthening of many of the hurricanes that move | |

| |through the Gulf of Mexico | |

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