Weather and ClimateWeather and Climate

Composition of the AtmosphereComposition of the Atmosphere

The atmosphere is a mixture of gases, liquids, and suspended solids that The atmosphere is a mixture of gases, liquids, and suspended solids that surrounds our planetsurrounds our planet

– Gases-Gases- include nitrogen, oxygen, carbon dioxide, water vapor and trace include nitrogen, oxygen, carbon dioxide, water vapor and trace gasesgases Mostly nitrogen (78%) and oxygen (21%)Mostly nitrogen (78%) and oxygen (21%) Even though the air thins with altitude, the proportion of gases Even though the air thins with altitude, the proportion of gases

remains the same through the first Kmremains the same through the first Km– Water vapor-Water vapor- enters the air by evaporation from the ocean & other enters the air by evaporation from the ocean & other

water sourceswater sources Amount of water vapor varies from 0 to 4% (depends on location, Amount of water vapor varies from 0 to 4% (depends on location,

season, and time of day)season, and time of day) Clouds, fog, and dew are caused by water vapor in the airClouds, fog, and dew are caused by water vapor in the air

– Suspended solids-Suspended solids- include dust, sea-salt, smoke, pollen, bacteria, and include dust, sea-salt, smoke, pollen, bacteria, and chemicals from industry & transportationchemicals from industry & transportation Cause hazy skies Cause hazy skies Act as Act as condensation nucleicondensation nuclei, where water vapor condenses on them , where water vapor condenses on them

to form clouds, fog , and raindrops to form clouds, fog , and raindrops

Structure of the AtmosphereStructure of the Atmosphere

The atmosphere is divided into layers based on changes in The atmosphere is divided into layers based on changes in temperaturetemperature– Troposphere-Troposphere- Begins at sea level and extends approximately 8 to Begins at sea level and extends approximately 8 to

18 kilometers depending on location and season18 kilometers depending on location and season– Stratosphere-Stratosphere- Extends Extends from the from the tropopausetropopause to an to an altitude of about 50 Km altitude of about 50 Km – Mesosphere-Mesosphere- Extends from Extends from the the stratopause stratopause to about 80to about 80 Km above the Earth’s surfaceKm above the Earth’s surface– Thermosphere-Thermosphere- Begins after Begins after the the mesopausemesopause, but has no , but has no definite upper limitdefinite upper limit

TroposphereTroposphere

Begins at sea level and extends approximately 8 to Begins at sea level and extends approximately 8 to 18 kilometers depending on location and season18 kilometers depending on location and season

Contains about 75% of the Contains about 75% of the gases in the atmosphere and gases in the atmosphere and most of the dust & water vapormost of the dust & water vapor Layer where weather occursLayer where weather occurs Since the atmosphere is Since the atmosphere is mainly heated from the Earth’s mainly heated from the Earth’s surface, temperature decreasessurface, temperature decreases with altitude with altitude

StratosphereStratosphere

Layer of the atmosphere extending outward from Layer of the atmosphere extending outward from the the tropopausetropopause to about 50 km to about 50 km

Strong eastward winds, called the Strong eastward winds, called the jet streamjet stream, blow , blow in a narrow band in this layerin a narrow band in this layer

A special form of oxygen, called A special form of oxygen, called ozoneozone, is found in , is found in this layerthis layer– Most is located in theMost is located in the ozone layer ozone layer– Absorbs harmful ultraviolet radiation from the sunAbsorbs harmful ultraviolet radiation from the sun

Temperature increases with altitude due to the Temperature increases with altitude due to the absorption of solar energy by ozoneabsorption of solar energy by ozone

MesosphereMesosphere

Atmospheric layer that extends Atmospheric layer that extends from the from the stratopause stratopause to about to about 80 Km above the Earth’s surface80 Km above the Earth’s surface

Protects the Earth from Protects the Earth from meteoroidsmeteoroids

Temperatures drop with altitude Temperatures drop with altitude to about -100to about -100°C, making it the °C, making it the ccoldest zone in the atmosphereoldest zone in the atmosphere

ThermosphereThermosphere Begins at about 80 Km, after the Begins at about 80 Km, after the mesopausemesopause, , but has no definite upper limitbut has no definite upper limit Temperatures increase rapidly with height due to the absorption of Temperatures increase rapidly with height due to the absorption of

solar energysolar energy Subdivided into two layers:Subdivided into two layers:

– Ionosphere-Ionosphere- (lower layer)(lower layer) Extends from 80 to 550 Km above Earth’sExtends from 80 to 550 Km above Earth’s surfacesurface Layer of electrically charged particles that Layer of electrically charged particles that reflect radio waves and produce aurorasreflect radio waves and produce auroras

– Exosphere-Exosphere- (upper layer)(upper layer) Begins 550 KmBegins 550 Km above the surface and extends for thousands of above the surface and extends for thousands of

kilometerskilometers Artificial satellites orbit the Earth in this layerArtificial satellites orbit the Earth in this layer Layer in which solar winds take placeLayer in which solar winds take place

Measuring Air TemperatureMeasuring Air Temperature Air temperature-Air temperature- A measure of the average speed of the A measure of the average speed of the

random motion of air moleculesrandom motion of air molecules– The higher the temperature, the faster the molecules moveThe higher the temperature, the faster the molecules move

Thermometer-Thermometer- Instrument used to measure temperature Instrument used to measure temperature– Works on the principle that most materials expand with increasing Works on the principle that most materials expand with increasing

temperaturestemperatures– As the temperature rises, liquid in the bulb expands into the stem of As the temperature rises, liquid in the bulb expands into the stem of

the thermometerthe thermometer Temperature scales-Temperature scales- Air temperature can be measured in Air temperature can be measured in

Fahrenheit (Fahrenheit (°F), Celsius (°C), or Kelvin (°K)°F), Celsius (°C), or Kelvin (°K)

– Fahrenheit to Celsius Fahrenheit to Celsius °C = 5/9 (°F - 32°)°C = 5/9 (°F - 32°)– Celsius to Fahrenheit Celsius to Fahrenheit °F = 9/5 °C + 32°°F = 9/5 °C + 32°– Celsius to Kelvin Celsius to Kelvin °K = °C + 273° °K = °C + 273°

Heating the AtmosphereHeating the Atmosphere Almost all of the energy Almost all of the energy heating our atmosphere heating our atmosphere comes from the sun comes from the sun (called (called radiant energyradiant energy)) Not all of the sun’s radiant Not all of the sun’s radiant energy reaches Earth’s surface; energy reaches Earth’s surface; some is reflected back into some is reflected back into

space,space, scattered, or absorbed by gases scattered, or absorbed by gases and clouds in the atmosphereand clouds in the atmosphere Solar energy which reaches the Solar energy which reaches the

Earth’s surface heats the Earth’s surface heats the atmosphere in one of three atmosphere in one of three ways: radiation, conduction, or ways: radiation, conduction, or convection convection

RadiationRadiation

Radiation-Radiation- The transfer of energy by The transfer of energy by electromagnetic waves such as lightelectromagnetic waves such as light– Can travel through a vacuumCan travel through a vacuum– When the sun’s radiant energy is absorbed by When the sun’s radiant energy is absorbed by

earth, it is changed into heatearth, it is changed into heat

ConductionConduction

Conduction-Conduction- The direct transfer of heat The direct transfer of heat energy from one substance to anotherenergy from one substance to another

1.1. Earth’s surface is warmed by radiant energyEarth’s surface is warmed by radiant energy2.2. Air coming in contact with Earth’s warm surface Air coming in contact with Earth’s warm surface

is heated by conductionis heated by conduction

Due to conduction, airDue to conduction, air temperatures are usually temperatures are usually higher the closer you arehigher the closer you are to the ground to the ground

ConvectionConvection

Convection-Convection- The transfer of heat energy The transfer of heat energy in a fluid ( gas or liquid)in a fluid ( gas or liquid)

1.1. Causes warmer fluids to rise in colder onesCauses warmer fluids to rise in colder ones

2.2. Convection currents in the atmosphere are caused Convection currents in the atmosphere are caused by the unequal heating of the Earth by the sunby the unequal heating of the Earth by the sun

3.3. Most of the heat energy in the atmosphere is Most of the heat energy in the atmosphere is transferred by convection currents transferred by convection currents

Global Temperature VariationsGlobal Temperature Variations

The temperature of the air can be affected by The temperature of the air can be affected by many factorsmany factors

Amount of sunlightAmount of sunlight

WindWind

LatitudeLatitude

AltitudeAltitude

Proximity to oceans and other water bodiesProximity to oceans and other water bodies

Seasons on EarthSeasons on Earth

The different seasons are caused by the The different seasons are caused by the Earth being tilted 23 ½ degrees on its axisEarth being tilted 23 ½ degrees on its axis

The tilt of the Earth on its axis, in The tilt of the Earth on its axis, in conjunction with it’s rotational path around conjunction with it’s rotational path around the sun, causes an unequal distribution of the sun, causes an unequal distribution of light and light and

heat at theheat at the

surface surface

SolsticesSolstices

SolsticeSolstice refers to the time when the sun seems to refers to the time when the sun seems to stop moving higher in the sky each daystop moving higher in the sky each day

On the solstice the Earth’s axis is pointing toward On the solstice the Earth’s axis is pointing toward the sun in one hemisphere and away from the sun the sun in one hemisphere and away from the sun in the otherin the other– Summer solstice-Summer solstice- First day of summer in the Northern First day of summer in the Northern

Hemisphere (June 20Hemisphere (June 20thth or 21 or 21stst)) Northern Hemisphere tilted toward the sunNorthern Hemisphere tilted toward the sun Direct rays located at 23 ½ Direct rays located at 23 ½ ° north latitude (Tropic of Cancer)° north latitude (Tropic of Cancer) Longest day of the year in Northern HemisphereLongest day of the year in Northern Hemisphere

– Winter solstice-Winter solstice- First day of winter in the Northern First day of winter in the Northern Hemisphere (December 21Hemisphere (December 21stst or 22 or 22ndnd)) Northern Hemisphere tilted away from the sunNorthern Hemisphere tilted away from the sun Direct rays located at 23 ½ Direct rays located at 23 ½ ° south latitude (Tropic of Capricorn)° south latitude (Tropic of Capricorn) Shortest day of the year in Northern HemisphereShortest day of the year in Northern Hemisphere

EquinoxesEquinoxes EquinoxEquinox means equal nightmeans equal night On the equinox, the Earth’s axis is not tilted On the equinox, the Earth’s axis is not tilted

toward the sun in either hemispheretoward the sun in either hemisphere At the equinoxes, day and night are of equal At the equinoxes, day and night are of equal

length all over the worldlength all over the world Direct rays of the sun located at Direct rays of the sun located at the equatorthe equator

– Autumnal equinox-Autumnal equinox- First day of First day of fall (September 22fall (September 22ndnd or 23 or 23rdrd))– Vernal equinox-Vernal equinox- First day of First day of spring (March 20spring (March 20thth or 21 or 21stst))

Mapping TemperaturesMapping Temperatures

Isotherms-Isotherms- Lines drawn on weather maps to Lines drawn on weather maps to

show places that have the same temperature show places that have the same temperature

at a given timeat a given time– One isotherm is usually drawn on a map for One isotherm is usually drawn on a map for

each 10each 10° difference in temperature° difference in temperature– Isotherms are similar to contour lines in that Isotherms are similar to contour lines in that

they each represent a unique measurement and they each represent a unique measurement and as a result won’t touch or cross as a result won’t touch or cross

How Isotherms are Shown on How Isotherms are Shown on Weather MapsWeather Maps

Isotherms showing 10° differences in temperature

Creating color bands between isotherms

Atmospheric PressureAtmospheric Pressure

Air pressure-Air pressure- Measure of the force of the Measure of the force of the atmosphere pressing down on Earth’s surfaceatmosphere pressing down on Earth’s surface

The pressure at any point on the Earth is equal to The pressure at any point on the Earth is equal to the weight of the air directly above that pointthe weight of the air directly above that point

Air pressure depends on the density of the air - the Air pressure depends on the density of the air - the denser the air, the higher the pressuredenser the air, the higher the pressure

Differences in air pressure cause Differences in air pressure cause

winds and changes in the weatherwinds and changes in the weather

Factors Affecting Air PressureFactors Affecting Air Pressure

Air pressure is affected by three factorsAir pressure is affected by three factors1.1. TemperatureTemperature

Since the gas molecules in warm air are farther apart than in Since the gas molecules in warm air are farther apart than in cold air, warm air is lighter (less dense) than cold aircold air, warm air is lighter (less dense) than cold air

When warm air replaces cold air, the pressure decreasesWhen warm air replaces cold air, the pressure decreases If cold air replaces warm air, the pressure increasesIf cold air replaces warm air, the pressure increases

2.2. Water vapor content (humidity)Water vapor content (humidity) The more water vapor the air contains, the lighter it isThe more water vapor the air contains, the lighter it is Humid air weighs less (has less pressure) than dry airHumid air weighs less (has less pressure) than dry air

3.3. Elevation (altitude) Elevation (altitude) As elevation increases, the air becomes thinnerAs elevation increases, the air becomes thinner (less dense)(less dense) Air pressure decreases with elevationAir pressure decreases with elevation

Measuring Air PressureMeasuring Air Pressure

Barometer-Barometer- Instrument used to measure air Instrument used to measure air pressure (two types)pressure (two types)– Aneroid barometers-Aneroid barometers- consist of a thin flexible can with consist of a thin flexible can with

a pointer attacheda pointer attached– Mercury barometers-Mercury barometers- use a glass tube filled with use a glass tube filled with

mercurymercury The average air pressure at sea level is 30.00 The average air pressure at sea level is 30.00

inches of mercuryinches of mercury Barometric readings drop about 1 inch for every Barometric readings drop about 1 inch for every

1000 feet above sea level1000 feet above sea level

Air Pressure Readings Air Pressure Readings on Weather Mapson Weather Maps

Weather maps use Weather maps use isobarsisobars to show areas that to show areas that

have the same air pressure at a given timehave the same air pressure at a given time– Pressure gradient-Pressure gradient- the rate of change between the rate of change between

two isobarstwo isobars– Isobars close together represent a steep gradient Isobars close together represent a steep gradient

(expect winds)(expect winds)– Isobars far apart show a weak Isobars far apart show a weak

gradient (expect calm air)gradient (expect calm air)

Air Pressure & the WeatherAir Pressure & the Weather

Barometers are used to forecast the weatherBarometers are used to forecast the weather Air pressure increases when large masses of air come Air pressure increases when large masses of air come

together in the upper atmospheretogether in the upper atmosphere– Prevents warm, moist air from risingPrevents warm, moist air from rising– Expect fair skies with no precipitationExpect fair skies with no precipitation

Pressure decreases when large air masses in the upper Pressure decreases when large air masses in the upper atmosphere move apartatmosphere move apart

– Causes warm air to riseCauses warm air to rise– Expect cloudy, rainy weatherExpect cloudy, rainy weather

In general:In general: Low pressure- warm, humid airLow pressure- warm, humid air High pressure- cool, dry airHigh pressure- cool, dry air Falling pressure- expect bad weatherFalling pressure- expect bad weather Rising pressure- expect good weatherRising pressure- expect good weather

WindsWinds

Winds result from the unequal heating of the Winds result from the unequal heating of the atmosphere by the sun atmosphere by the sun – This causes pressure differencesThis causes pressure differences

Winds occur when air moves from areas of Winds occur when air moves from areas of high pressure to areas of lowhigh pressure to areas of low

The bigger the difference in The bigger the difference in

pressure (the larger the gradient), pressure (the larger the gradient),

the stronger the windsthe stronger the winds

Wind DirectionWind Direction

Wind Vane-Wind Vane- Device used to determine wind Device used to determine wind directiondirection– Points in the direction the wind is blowing fromPoints in the direction the wind is blowing from

Windsock-Windsock- Cloth bag-like device used to Cloth bag-like device used to determine wind direction and speeddetermine wind direction and speed– The end of the windsock points in the direction the wind The end of the windsock points in the direction the wind

is blowing to is blowing to Winds are named for the direction from which they Winds are named for the direction from which they

comecome– A northerly wind would blow from the north to the south A northerly wind would blow from the north to the south

Coriolis ForceCoriolis Force

Coriolis Force-Coriolis Force- an effect produced by Earth’s an effect produced by Earth’s

rotation which causes objects in motion to be rotation which causes objects in motion to be

deflecteddeflected– Deflection is to the right in the Northern Hemisphere and Deflection is to the right in the Northern Hemisphere and

to the left in the Southernto the left in the Southern– The further from the equator, the greater the deflectionThe further from the equator, the greater the deflection– Cause surface winds to blow at an angle to the isobarsCause surface winds to blow at an angle to the isobars

The Coriolis Force has no effect on the way water swirls when you flush a toilet

Wind SpeedWind Speed

Anemometer-Anemometer- Instrument used to Instrument used to measure wind speedmeasure wind speed Factors that effect wind speedFactors that effect wind speed

– Pressure gradients-Pressure gradients- The steeper the gradient, The steeper the gradient, the stronger the windsthe stronger the winds

– Friction with the Earth’s surface-Friction with the Earth’s surface- Winds travel Winds travel faster over smooth, obstacle free surfacesfaster over smooth, obstacle free surfaces

– Season-Season- Wind speeds are generally greater in Wind speeds are generally greater in winter than in summerwinter than in summer

Wind Chill FactorWind Chill Factor

Wind Chill Factor-Wind Chill Factor- Perceived temperature Perceived temperature to the human body based on both wind to the human body based on both wind speed and air temperaturespeed and air temperature

The stronger the wind, the colder it feelsThe stronger the wind, the colder it feels

Types of WindsTypes of Winds

There are two types of winds- local & globalThere are two types of winds- local & global Local winds-Local winds- Movement of air caused by Movement of air caused by

differences in the heating and cooling rates of land differences in the heating and cooling rates of land and waterand water

Global Winds-Global Winds- Large scale movement of air Large scale movement of air caused by the unequal heating of the earth’s caused by the unequal heating of the earth’s surfacesurface– Convection currents in the atmosphere cause cold, Convection currents in the atmosphere cause cold,

dense air from areas near the poles to sink and move dense air from areas near the poles to sink and move along the surface, forcing warm air near the equator along the surface, forcing warm air near the equator aloftaloft

– Create a worldwide system of wind and ocean currentsCreate a worldwide system of wind and ocean currents

Local WindsLocal Winds

Sea breeze-Sea breeze- Winds occurring during the day when Winds occurring during the day when cool, dense air cool, dense air

from over the water flowsfrom over the water flows

inward and forces the warm inward and forces the warm

air over the land to riseair over the land to rise Land breeze-Land breeze- Winds occurring at night when cool Winds occurring at night when cool

air from over the land flows seaward and forces air from over the land flows seaward and forces the warm air over the ocean tothe warm air over the ocean to

riserise

Local WindsLocal Winds

Monsoons-Monsoons- A major land and sea breeze A major land and sea breeze that reverses direction based on seasonal that reverses direction based on seasonal temperature changestemperature changes– During one season winds blow from the ocean During one season winds blow from the ocean

onto the land and during another they blow from onto the land and during another they blow from the land back over the waterthe land back over the water

– Warm, moist air blowing from the ocean results Warm, moist air blowing from the ocean results in a rainy season in a rainy season

Global WindsGlobal Winds

Major wind patterns produced by the unequal heating of Major wind patterns produced by the unequal heating of Earth’s surface in combination with its rotationEarth’s surface in combination with its rotation

Winds blow from areas of high pressure to those of low Winds blow from areas of high pressure to those of low pressure pressure

Types of global winds:Types of global winds:– Trade Winds-Trade Winds- Blow toward the equatorial low (0Blow toward the equatorial low (0° latitude) from the ° latitude) from the

subtropical highs (30° lat.)subtropical highs (30° lat.)– Prevailing Westerlies-Prevailing Westerlies- Blow from the subtropical highs (30° lat.) to Blow from the subtropical highs (30° lat.) to

the sub-polar lows (60° lat.) the sub-polar lows (60° lat.) – Polar Easterlies-Polar Easterlies- Cold, dense air mass which moves from the Cold, dense air mass which moves from the

polar highs (90° lat.) to the sub-polar lows (60° lat.) polar highs (90° lat.) to the sub-polar lows (60° lat.)

Global Wind PatternsGlobal Wind Patterns

Relative HumidityRelative Humidity

Humidity-Humidity- Water vapor or moisture in the air Water vapor or moisture in the air Relative humidity-Relative humidity- Percent of moisture the air is Percent of moisture the air is

holding relative to the amount that it can hold at a holding relative to the amount that it can hold at a particular temperatureparticular temperature

% Relative humidity =% Relative humidity = Amount of water vapor in the air Amount of water vapor in the air Amount of water vapor the air can Amount of water vapor the air can hold at that temperaturehold at that temperature

Saturated air-Saturated air- Air with a relative humidity of 100% Air with a relative humidity of 100%

Measuring Relative HumidityMeasuring Relative Humidity

Hygrometer-Hygrometer- Instrument used to measure relative Instrument used to measure relative humidityhumidity

Psychrometer-Psychrometer- A hygrometer that determines A hygrometer that determines relative humidity based on cooling that occurs due relative humidity based on cooling that occurs due to evaporationto evaporation– Consists of two thermometers:Consists of two thermometers: a wet bulb and a dry bulba wet bulb and a dry bulb– Once the temperature isOnce the temperature is determined on both thermometers,determined on both thermometers, a chart is then used to determine a chart is then used to determine the relative humiditythe relative humidity

Condensation and Dew PointCondensation and Dew Point

Condensation-Condensation- The formation of liquid drops from The formation of liquid drops from water vapor. water vapor. – It is the process which creates cloudsIt is the process which creates clouds– Necessary for rain and snow formation Necessary for rain and snow formation – Condensation nuclei-Condensation nuclei- Tiny particles of salt or dust that Tiny particles of salt or dust that

water vapor in the air condenses around water vapor in the air condenses around

Dew point-Dew point- The temperature at which saturation The temperature at which saturation occursoccurs– This is the temperature that a sample of air would need This is the temperature that a sample of air would need

to be cooled so that its relative humidity would be 100% to be cooled so that its relative humidity would be 100%

Four ways that air can be cooled Four ways that air can be cooled to its dew pointto its dew point

1.1. Contact with Contact with a colder a colder surfacesurface

2.2. Radiating Radiating heat heat

3.3. Mixing with Mixing with colder aircolder air

4.4. Expanding Expanding when it riseswhen it rises

Forms of CondensationForms of Condensation

Dew-Dew- Water droplets forming on surfaces Water droplets forming on surfaces when the air is saturated and temperatures when the air is saturated and temperatures are above freezingare above freezing

Frost-Frost- Ice crystals that form on surfaces Ice crystals that form on surfaces when the air is saturated and temperatures when the air is saturated and temperatures are at or below freezingare at or below freezing

Forms of CondensationForms of Condensation

Fog-Fog- A suspension of tiny water droplets in A suspension of tiny water droplets in the air, at or near the Earth’s surface the air, at or near the Earth’s surface

– Occurs when a surface layer of air is cooled Occurs when a surface layer of air is cooled below the dew pointbelow the dew point

– Basically a stratus cloud that has its base at or Basically a stratus cloud that has its base at or near the groundnear the ground

Forms of CondensationForms of Condensation Clouds-Clouds- A suspension of tiny water A suspension of tiny water

droplets in the airdroplets in the air– Form when moisture in the air condenses on Form when moisture in the air condenses on

small particles of dust or saltsmall particles of dust or salt– Classified based on shape and altitudeClassified based on shape and altitude– There are three main types of clouds:There are three main types of clouds:

1.1. CumulusCumulus

2.2. StratusStratus

3.3. CirrusCirrus

Types of CloudsTypes of Clouds

1.1. Cumulus-Cumulus- Fluffy, white clouds with flat bottomsFluffy, white clouds with flat bottoms Usually indicate fair weatherUsually indicate fair weather

2.2. Stratus-Stratus- Smooth gray clouds that cover the Smooth gray clouds that cover the entire skyentire sky Usually associated with rain or drizzleUsually associated with rain or drizzle

3.3. Cirrus-Cirrus- Feathery clouds made of ice crystalsFeathery clouds made of ice crystals Often indicate that precipitation will Often indicate that precipitation will occur within several hoursoccur within several hours

PrecipitationPrecipitation

Precipitation-Precipitation- Any form of water that falls from the Any form of water that falls from the atmosphere to Earthatmosphere to Earth

Forms when water vapor changes back to liquid Forms when water vapor changes back to liquid water (water (condensationcondensation) or to ice crystals ) or to ice crystals ((sublimationsublimation))

The form of precipitation that reaches the ground The form of precipitation that reaches the ground depends on the temperature conditions it depends on the temperature conditions it encounters on the way and the amount of encounters on the way and the amount of impurities in the airimpurities in the air– The more impurities, the colder the air must be in order The more impurities, the colder the air must be in order

to form ice crystalsto form ice crystals

Types of PrecipitationTypes of Precipitation

Drizzle-Drizzle- Fine rain with small, slowly Fine rain with small, slowly falling water dropletsfalling water droplets

Rain-Rain- Large water droplets that form Large water droplets that form when water vapor condenses in the when water vapor condenses in the clouds then falls to the groundclouds then falls to the ground

Snow-Snow- Flat, six-sided ice crystals that Flat, six-sided ice crystals that form when water vapor changes directly form when water vapor changes directly into ice crystals (into ice crystals (sublimationsublimation))

Types of PrecipitationTypes of Precipitation

Hail-Hail- Irregularly shaped balls or lumps of ice Irregularly shaped balls or lumps of ice and snow that form in cumulonimbus cloudsand snow that form in cumulonimbus clouds– Form from ice pellets, trapped in updrafts, that Form from ice pellets, trapped in updrafts, that

get repeatedly coated with water dropletsget repeatedly coated with water droplets– Associated with summertime thunderstormsAssociated with summertime thunderstorms

Types of PrecipitationTypes of Precipitation

Sleet-Sleet- Grains of ice or frozen raindrops that Grains of ice or frozen raindrops that form when rain passes through a cold layer form when rain passes through a cold layer of air and freezes into ice pelletsof air and freezes into ice pellets– Raindrops fall through a layer of air which is Raindrops fall through a layer of air which is

3232°F or colder°F or colder– Occurs most often in the winter when warm air Occurs most often in the winter when warm air

is forced over ais forced over a

layer of cold air layer of cold air Sleet is not the same as freezing rain.Freezing rain falling as a liquid but freezesupon contact with cold (below 32°) surfaces

StormsStorms

Storms are violent disturbances in the atmosphere marked Storms are violent disturbances in the atmosphere marked by sudden changes in air pressure and rapid air by sudden changes in air pressure and rapid air movementsmovements

Types of storms:Types of storms:– Rainstorms & Snowstorms-Rainstorms & Snowstorms- results in extended periods of results in extended periods of

precipitation precipitation – Thunderstorms-Thunderstorms- heavy rain storms accompanied by thunder and heavy rain storms accompanied by thunder and

lightninglightning– Hurricanes-Hurricanes- storm with violent winds (greater than 75 mph) and storm with violent winds (greater than 75 mph) and

heavy rain that forms over tropical oceans during late summer and heavy rain that forms over tropical oceans during late summer and early fallearly fall

– Tornadoes-Tornadoes- A whirling, funnel-shaped cloud that develops in A whirling, funnel-shaped cloud that develops in cumulonimbus clouds and produce winds of up to 300 mphcumulonimbus clouds and produce winds of up to 300 mph

Factors to consider when trying to Factors to consider when trying to make a weather forecastmake a weather forecast

Sequence of cloud formation-Sequence of cloud formation- Cirrus clouds Cirrus clouds changing to low level stratus clouds warn of changing to low level stratus clouds warn of upcoming precipitationupcoming precipitation

Wind direction-Wind direction- Winds from the NE, E, and S Winds from the NE, E, and S usually bring unsettled airusually bring unsettled air

Changes in air pressure-Changes in air pressure- A rising barometer A rising barometer usually means fair weather, but falling readings usually means fair weather, but falling readings are known for stormy conditions are known for stormy conditions

Air Temperature-Air Temperature- Will determine the type of Will determine the type of precipitation that fallsprecipitation that falls