3.  Weather refers to the state of atmosphere at a specific time and place.  Weather describes conditions such as air pressure, wind, temperature, and the amount of moisture in the air.  Weather is the result of heat and Earth’s air and water.

4.  When air is heated, it expands and becomes less dense. This creates lower pressure.

5.  Molecules making up air are closer together in cooler temperatures, creating high pressure. Wind blows from higher pressure toward lower pressure.  Wind results because air moves from regions of high pressure to regions of low pressure.  Wind direction can be measured by using a wind vane (an arrow that points in the direction toward which the wind is blowing).  Wind speed can be measured using an anemometer (rotating cups that spin faster when the wind is blowing).

7. Anemometer

8.  Heat evaporates water into the atmosphere.  Water vapor molecules fit into spaces among the molecules that make up air.  The amount of water vapor present in the air is called humidity.  Warmer air can have more water vapor than cooler air can because water vapor doesn’t easily condense in warm air.

9.  A measure of the amount of water vapor present in the air compared to the amount needed for saturation at a specific temperature.

10.  The temperature at which air is saturated and condensation forms is the dew point.  The dew point changes with the amount of water vapor in the air.

12.  When the relative humidity reaches 100%, the air is saturated and water vapor soon begins to condense in tiny droplets around small particles such as dust and salt.  These droplets of water are so small that they remain suspended in the air.  Billions of these droplets form a cloud.

15.  3 main cloud types: - stratus - cumulus - cirrus

16.  Stratus: forms layers or smooth even sheets in the sky  Forms at low altitudes  May be associated with fair weather, rain or snow  When air is cooled to its dew point near the ground, it forms a stratus cloud called fog.

17. Stratus Clouds

18.  Cumulus: masses of puffy, white clouds, often with flat bases/great heights  Associated with fair weather of thunderstorms

19. Cumulus Clouds

20.  Cirrus: appear fibrous or curly/high, thin, white, feathery clouds made of ice crystals  Associated with fair weather/can indicated approaching storms

21. Cirrus Clouds

22.  Clouds associated with rain or snow has the word nimbus attached to them.  Nimbus is Latin for “dark rain cloud”

23. Stratus Cumulus Cirrus

25. TThe prefix cirro- describes high clouds TThe prefix alto- describes middle-elevation clouds TThe prefix strato- describes clouds at low elevations

26. WWater falling from clouds is precipitation. AAir temperature determines whether water forms rain, snow, sleet or hail – the four main types of precipitation.

27.  Hail is precipitation in the form of lumps of ice.  Hail forms in the cumulonimbus clouds of a thunderstorm when water freezes in layers around a small nucleus of ice.

28. 1. What are thick puffy clouds called? 2. What are high, feathery clouds usually associated with fair weather? 3. What is the temperature at which air is saturated with water vapor cools and condenses into water droplets. 4. The highest clouds are known as _______. 5. What means the air is holding all the water vapor it can? 6. What are low gray clouds that produce drizzle? 7. ______ ________ - a measure of how much water vapor the air is holding compared to how much it can hold at a specific temperature. 8. ***When can the air hold more water vapor?

29. 1. Name three factors that make weather. 2. When water droplets form around dust particles & become heavy enough to fall out of the clouds, we have ___________. 3. What is a large body of air with the same properties as Earth’s surface over which it develops? 4. What is rain, snow, sleet and hail? 5. _____ is raindrops that pass through a layer of freezing air near the ground. 6. ***When the air near the ground cools to its dew point what happens sometimes? 7. ***Why does dew form on grass in the early morning? 8. ***Compare sleet and hail.

31.  Because of the movement of air and movement in the atmosphere, weather constantly changes.  Air mass – large body of air that has properties similar to the part of Earth’s surface over which it develops.  Air mass that develops over land is dry compared with one that develops over water.  Winds blow away from a center of high pressure.  High-pressure areas are associated with fair weather and are called anticyclones.

32.  A boundary between two air masses of different density, moisture, or temperature is called a front.

33.  A cold front can advance rapidly. Thunderstorms often form as warm air is suddenly lifted up over the cold air.  Warm air slides over colder air along a warm front, forming a boundary with gentle slope. This can lead to hours, if not days, of wet weather.

34.  The term occlusion means “closure”. Colder air forces warm air upward, forming an occluded front that closes off the warm air from the surface.  A stationary front results when neither cold air nor warm air advances.

35.  Sinking, rain-cooled air and strong updrafts of warmer air cause the strong winds associated with thunderstorms.  Hail from a thunderstorm can dent cars and the aluminum siding on houses.  Thunder results from the rapid heating of air around a bolt of lightning. Lightning can reach temperatures more than five times the temperature of the surface of the sun.  This extreme heat causes air around the lightning to expand rapidly.

36.  A tornado is a violently rotating column of air in contact with the ground.  Tornados rarely exceed 200m in diameter and usually last only a few minutes, they often are extremely destructive.  Hurricanes – the most powerful storm; a large, swirling, low-pressure system that forms over the warm Atlantic Ocean.  Similar storms are called typhoons in the Pacific Ocean and cyclones in the Indian Ocean.  Blizzards are severe storms that occur in the winter.

37.  The National Weather Service classifies a winter storm as a blizzard if winds are 36mph (56km/h), the temperature is low, the visibility is less than 400m in falling or blowing snow, and if these conditions persist for three hours or more.

38.  When severe weather threatens, the National Weather Service issues a watch or warning.  During a severe thunderstorm or tornado warning, take shelter in the basement or a room in the middle of the house away from windows.  When a hurricane or flood watch is issued, be prepared to leave your home and move further inland.  During a blizzard stay indoors.

39. 1. A ______ forms where cold and warm air meet. 2. ____ _____ air usually means good weather because the heavy air makes it difficult for air to rise and clouds to form. 3. A line that connects points of equal temperature is _______. 4. _____ _____ systems form along fronts. 5. A _____ _____ often causes the formation of violent storms. 6. A ____ _____ pushes a ____ _____ up and may cause thunderstorms. 7. A stationary front may stay in an area several days producing _____ ______ and precipitation. 8. Why does high humidity cause discomfort in the summer?

40. 1. A ______ is a violent, whirling wind that moves over land in a narrow path. 2. Hurricanes form over _____ ______. 3. _____ and _____ are related because one may develop because of the other. 4. Whose job is to forecast weather using data collect from many sources? 5. What type of cloud often forms from a tornado? 6. A ____ _____ air mass forms off of the southeast coast of the US. 7. The build up of electrical charges in the clouds produces _______.

42. AA meteorologist is a person who studies the weather. MMeteorologists take measurements of temperature, air pressure, winds, humidity, and precipitation. IInstruments used by meteorologists to gather data and create maps to make weather forecasts: computers, weather satellites, and Doppler radar

43.  The National Weather Service depends on two sources for its information: -data collected from the upper atmosphere -data collected on the Earth’s surface  Meteorologists of the National Weather Service collect their information recorded by satellites, instruments attached to weather balloons and from radar.

44.  A station model shows the weather conditions at a specific location on Earth’s surface.

45. Station Model Symbols

47. AA line that connects points of equal temperature is called an isotherm. Iso- means “same” and therm- means “temperature”. AAn isobar is a line drawn to connect points of equal atmospheric pressure.