Presentation on theme: "Ch. 2 Weather Section 1 What is Weather? Section 2 Weather Patterns"— Presentation transcript:
1 Ch. 2 Weather Section 1 What is Weather? Section 2 Weather Patterns Section 3 Weather Forecasting
2 Section 1 What is Weather? Refers to the state of the atmosphere at a specific time and place
3 Weather FactorsDescribes conditions such as air pressure, wind, temperature, and humidity, or moisture in the air.The Sun provides almost all of Earth’s energy.Drives the Water CycleCauses wind to occur
4 Temperature Review Temperature is a measure of air molecule movement High temp. = Warm = air molecules move rapidlyLow temp. = Cold = air molecules move slowly
5 WindMovement of air in a specific direction = from regions of higher pressure to regions of lower pressureCool air is denser so higher pressureWarm air is less dense so lower pressure
7 Direction can be determined using a: Wind Vane - has an arrow that points in the direction from which wind is blowingWind Sock - has one open end that catches the wind, causing sock to point in the direction toward which wind is blowing
8 Wind speed can be measured using an: Anemometer - has rotating cups that spin faster when the wind is strong
9 Humidity The amount of water vapor present in the air Warm air can hold more water vapor than cool air.Water vapor condenses and sticks together when cooledExpressed as g/m3
10 Relative HumidityA measure of the amount of water vapor present in air compared to the amount needed for saturation at a specific temp.Expressed as a %
11 Saturation When relative humidity is 100% Or, in other words, when air is holding the maximum amount of water vapor it can hold at a certain temp.
12 Relative Humidity & Saturation Air at 25°C is saturated when it contains 22 g of water vapor per cubic meter of air.The relative humidity is 100 percent.
13 Relative Humidity & Saturation If air at 25°C contains 11 g of water vapor per cubic meter, the relative humidity is 50 percent.
14 Dew Point The temperature at which air is saturated and dew forms The dew point changes with the amount of vapor present in the air.When temperature drops, less water vapor can be present in the air.The vapor will condense into a liquid or ice crystals
15 Because land cools so quickly, air in contact with the cold ground can reach its dew point, causing dew to form on the ground.If the temp. is near 0 ˚C, frost will form.Condensation forms on the outside of a glass because the cold glass brings the air next to it down to its dew pt.
16 Forming CloudsClouds form when warm, moist air is forced upward, expands, and cools to its dew pointWater vapor condenses around tiny particles called condensation nuclei.Water droplets are so small that they stay suspended. Billions of these droplets form a cloud.
17 Ways in which air lifts and cools: Rays from the Sun heat the ground and the air next to it making it buoyant. The warm air rises and cools.As moist air moves over mountains, it is forced upward and cools.When cool air meets warm, moist air along frontal boundaries the warm air rises and cools.
19 Classifying Clouds Classified mainly by shape and height Shapes: Stratus - form layers, or smooth even sheets in the skyFog - stratus clouds that form near the groundCumulus - puffy, white clouds, often with flat basesCirrus - thin, white feathery clouds made of ice crystals
21 Rain- or Snow-Producing Clouds Have the word nimbus or nimbo attached to themSunlight usually cannot penetrate throughEx: cumulonimbus, nimbostratus
22 Precipitation Water falling from clouds 4 main types: RainSnowSleetHailForm is determined by air temperature
23 RainWhen the air is warm, water vapor forms raindrops that fall as rainSize depends on:Strength of updraftStronger = larger dropsRate of evaporationIf the air is dry, size can be reduced by evaporation before reaching the ground
24 SnowForms when the air temp. is so cold that water vapor changes directly to a solid
25 SleetForms when raindrops pass through a layer of freezing air near Earth’s surface
26 HailForms in cumulonimbus clouds when water vapor freezes in layers around a small nucleus of iceThe stronger the updraft, the larger the hailstoneMost hailstones are < 2.5 cm, but some can be as large as a softballCauses the most damage of all forms of precipitation
27 Question 1The state of the atmosphere at a specific time and place is __________.A. climateB. meteorologyC. seasonD. weather
28 Question 2 The amount of water vapor present in the air is __________. A. dewB. condensationC. fogD. humidity
31 Air MassA large body of air that has properties similar to the part of Earth’s surface over which it developedCan cover thousands of square kmDaily changes in Wx are due to the movement of air masses.
34 Highs and Lows Air pressure is measured using a barometer. Remember: Winds blow from high to low pressure areas.
35 Highs Winds blow away from a center of high pressure Earth’s rotation causes the wind to swirl in a CW dir.Called anticyclonesSinking motion in highs makes it difficult for air to rise and clouds to formHigh pressure usually signals good Wx.
36 Lows Winds blow toward a center of low pressure Earth’s rotation causes the wind to swirl in a CCW dir.Called cyclonesAir rises in a low causing clouds to form.Lows are usually associated w/ cloudy and/or rainy Wx.
37 Front Boundary b/w two air masses of diff. density, moisture, or temp. Cloudiness, ppt, and storms sometimes occur at frontal boundaries as air is lifted4 types:Cold, Warm, Occluded, StationaryNeed to know symbols!
38 Cold Front Occurs when colder air advances toward warm air Cold air wedges under warm air like a plow with a steep front causing air to lift and cool rapidlyGenerally produces heavy ppt that starts and stops abruptlyThunderstorms common; tornadoes may form
40 Warm FrontOccurs when lighter, warmer air advances over heavier, colder airUsually forms a boundary with a gentle slope causing air to lift and cool graduallyGenerally produces steady ppt that lasts for hours or days
46 Severe Weather Poses danger to people, structures, or animals Includes:ThunderstormsTornadoesHurricanesBlizzards
47 ThunderstormsForm in warm, moist air masses and along fronts whenever air lifts and cools rapidly forming cumulonimbus cloudsFalling raindrops cool the surrounding air. Cool, dense air sinks forming downdrafts.
48 Extremely powerful storms can produce large hailstones. Damage: Flash floodingStrong winds (>89 km/h = severe thunderstorm)HailStrong downdraftsLightningTornadoes
49 LightningOccurs when rapid movement of air w/in a storm cloud causes diff. parts of the cloud to become oppositely chargedLightning is the flow of current b/w regions of op. elec. charge.
50 Can occur w/in a cloud, b/w clouds, or b/w a cloud and the ground Can reach temp. of about 30,000 ˚C
51 ThunderResults from the rapid heating of air around a bolt of lightningThe extreme heating of air around lightning causes it to expand and contract rapidly, which forms sound waves heard as thunder
52 Tornadoes Violently rotating columns of air in contact with the ground Form at the base of cumulonimbus cloudsRanked according to the Fujita scale according to how much damage they cause (F0 - F5)
53 HurricanesLarge, swirling low-pressure systems that form over the warm Atlantic OceanCalled typhoons in the Pacific Ocean and cyclones in the Indian OceanMust have wind speeds >199 km/h
54 Ranked according to the Saffir-Simpson scale according to wind speed (Category 1 - Category 5) Damage:High windsTornadoesHigh wavesStorm surgesFloods
55 BlizzardsWinter storms that have winds ≥56 km/h, low temps., and visibility <400 m that persist for at least 3 hours
56 Watches vs. WarningsWatches - are issued when conditions are favorable for severe WxWarnings - are issued when severe Wx conditions already exist
57 Question 1 Water falling from clouds is _______________. A. Cloud coverB. DewC. FogD. Precipitation
58 Question 2A large body of air that has properties similar to the area over which it develops is ______________.An air massCloud coverFogFront
59 Question 3What is the boundary between two air masses of different density, moisture, or temperature called?How do you classify them?
65 Station Models Highs and Lows Show Wx conditions at a specific location on Earth’s surfaceCan include info. on up to 20 diff. Wx conditionsHighs and LowsDrawn as circles with the word “high” or “low” in the middle