DO NOW

Tell a friend what you feel like on humid days.

What time of year do we have humid days?

Chapter 2:

“Understanding Weather”

HumidityHumidity – the amount of water vapor in air Air’s ability to hold water vapor changes as

the temperature of the air changes.

Increased temperature means the air can hold more water.

Decreased temperature means the air can hold less water.

Relative Humidity

Relative Humidity –ratio of water vapor in the air to the maximum amount the air can hold2 factors that affect relative humidity:1. Temperature2. Water vapor

in the air

How to measure relative humidity? Psychrometer – a tool to measure relative

humidity; contains a wet and a dry bulb.

1) Wet-bulb thermometer –bulb covered with wet cloth

2) Dry-bulb thermometer –bulb is dry

Measuring Relative Humidity

The difference in temperature readings between the 2 thermometers is used to determine the relative humidity.

Determining Relative Humidity

Water in the Air Dew Point –temperature when the air can no longer hold any more water (gas condenses to a liquid)

Happens when relative humidity reaches 100%

DO NOWWrite the answer to this question in

the DO NOW section of your binder:• What is the relative humidity if the

temperature in the classroom today is 20oC on the dry bulb and 17oC on the wet bulb?

CloudsClouds are groups of millions of tiny water droplets or ice crystals

2 Steps to Cloud formation:1. Air rises 2. Air cools below the dew point, water

droplets form

Water droplets – form when water condenses

above 0 C

Ice crystals – form when water condenses

below 0 C

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Clouds Are Made Of…

Clouds

2) Shape:• Stratus clouds (sheets, stripes,

bands)• Cumulus clouds (clumpy & puffy)• Cirrus clouds

Clouds are classified by:

1) Altitude• Low clouds• Middle clouds• High clouds

*NIMBO or NIMBUS = clouds producing precipitation*

Low Clouds

Found below 2,000 meters & made of only water droplets

Three Types:1)Stratus Clouds2)Nimbostratus Clouds3)Stratocumulus Clouds

“Overcast”Ill-defined edgesIn layersBlock sun

Dark stratus cloudcontinuous rainGray, rainy days

Lumpy & Low lying Patches of clouds with some blue between.Flat (Doesn’t look like popcorn)

Found between 2,000 meters and 6,000 meters

They are made of water droplets or ice crystals

Alto- means “middle”

Four Types:1) Cumulus2) Cumulonimbus3) Altocumulus4) Altostratus

Middle Clouds

White & PuffyDistinct edges popcorn-like; NOT flat

Big & Dark cumulus cloud

Thunderstorm cloudsHail, tornadoesTallest clouds

anvil shaped top

Layered cumulus clouds Distinct cloud elementsPatchy, scattered, or in bands

Uniform & Scattered CoverageDifficult to detect individual features

High Clouds

Found above 6,000 mTemperature are very cold and made of ice crystals

Cirro- means “high”

Three Types:1) Cirrus Clouds2) Cirrocumulus Clouds3) Cirrostratus Clouds

Thin & feathery, wispy

Thick white wispyDistinct patchy or wavelike appearance

Sheet-like & cover entire skyUsually transparent

(sun/moon can easily be seen)

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Recap!!!

What is weather? What does it greatly depend on?Weather is the condition of the atmosphere at a certain time and place. It depends greatly on the amount of water in the air.

What is the difference between humidity and relative humidity?

Humidity is the amount of water vapor in the air. Relative humidity is the ratio of the amount of water vapor in the air to the maximum amount the air can hold.

Which two main cloud shapes are seen in this picture?

Stratus

Cumulus

A

B

Which two main cloud shapes are seen in this picture?

Cumulus

CirrusC

D

CirrusClouds

StratusClouds

Recap!!!What does nimbo or nimbus mean for clouds?

It produces precipitationWhat does stratus mean for clouds?They are layered

What are each of the following clouds made of? 1) Low Clouds 2) Middle Clouds 3) High Clouds

1) Water droplets only2) Water droplets/ice

crystals3) Ice crystals only

What are the two most common forms of precipitation? Rain and

snow

Air Masses

Air Masses – a very large volume of air that has a certain temperature & moisture content

When air masses meet, the less dense air mass rises over more dense air mass.

Since warm air is less dense, warm air masses usually rise above cold air masses

Front– the place where two or more air masses meet

The four main kinds of fronts are:

1) Cold Fronts2) Warm Fronts3) Occluded Fronts4) Stationary Fronts

Fronts

Cold FrontsCold air mass moves under a warm air

mass and pushes the air upCold air mass replaces warm air massMoves quick & brings heavy precipitation

Warm FrontsWarm air mass moves in over a cold air

mass leaving an area.

Warm air mass replaces cold air as it moves away

Bring light rain & followed by clear, warm weather

Cold air mass pushes Warm air mass replaceswarm air mass away a cold air mass

Visual

Warm air mass is caught between 2 cold air masses.

Brings cool temperatures, rain, and snow

Occluded Fronts

Cold air mass & a warm air mass move toward each other.

Neither has enough energy to push the other away.

Remain in same place causing cloudy weather

Stationary Fronts

Occluded Front = warm air mass is trapped between two cold air masses, which move together and push warm air away

Stationary Front = air masses stay in one place

Cyclone – air mass formed that has lower pressure than surrounding air. Air rises and cools Forecast: Clouds can form & cause rainy or stormy

weather

Anticyclone – air mass that has higher pressure than the surrounding air• Air sinks and gets warmer• Relative humidity decreases• Forecast: Warm sinking air brings dry, clear

weather

Air Pressure and Weather

Cyclones and anticyclones can affect each other. Air moving out from anticyclones move towards areas of low pressure. This movement can form a cyclone.

What does air mass depend on?

Recap!!!

Water Content (Moisture) & Temperature

What are the four different kinds of fronts?

Cold FrontsWarm FrontsOccluded FrontsStationary Fronts

Recap!!! What is the difference between Cyclones

and Anticyclones?• Cyclones lower pressure than surrounding air

• Cools as it rises.

• Anticyclones higher pressure than surrounding air

• Warms as it sinks.

How are front and air masses related?• A front is where two or more air masses meet.

Therefore, without air masses…there would be nofronts.

What are the different types of severe weather?

1.) Thunderstorms

2. Hurricanes

3. Tornadoes

Thunderstorms –intense storm with strong winds, heavy rain, lightening, & thunder

often along cold fronts

Conditions required:1) Warm, moist air near Earth’s surface2) Unstable area of the atmosphere

Thunderstorms

Thunderstorms

4 Steps to a Formation of a Thunderstorm

1. cold air above warm air (unstable)

2. Warm air rises & mixes with cool air

3. water vapor condenses & forms cumulus clouds

4. If warm air keeps rising, clouds become dark cumulonimbus clouds

What is the difference between a severe thunderstorm watch and a

severe thunderstorm warning?

• A severe thunderstorm watch is issued by the National Weather Service when the weather conditions are such that a severe thunderstorm is likely to develop.

• A severe thunderstorm warning is issued when a severe thunderstorm has been sighted or indicated by weather radar. At this point, the danger is very serious and everyone should go to a safe place, turn on a battery-operated radio or television, and wait for further information

Thunderstorm Safety

•Avoid touching metal objects•Install metal lightning rods•Find a low area away from trees•Stay away from water

• Number of days each year in which thunderstorms occur. • Note hightest (90) in Florida.

Lightning5 steps to the formation of lightning:

1. As a cloud grows bigger, parts begin to develop electrical charges

• Upper parts = positively charged

• Lower parts = negatively charged

2. When the charge difference gets big enough, electricity flows from one area to another (between the clouds) or to the ground

Lightening Video # 1 Simulation of Lightening

Thunder

4 Steps to the Formation of Thunder

1. When lightning moves through the air, the air gets very hot

2. hot air expands rapidly and vibrates

3. Vibrations release energy in the form of sound waves, called thunder.

Hurricanes Hurricanes – large, rotating tropical weather systems

Wind speeds over 120 km/h Can be 160 km to 1,500 km in diameter and travel thousands of miles

Most powerful storms on EarthAlso called typhoons & cyclones

Where are they formed?Over warm, tropical oceans

Hurricanes5 Steps in the Formation of a Hurricane 1. Begins as a group of thunderstorms over

tropical waters (Tropical Disturbance)

2. Winds traveling indifferent directions meet & cause the storm to spin (Tropical Depression)

counterclockwise in the North clockwise in the South

Tropical Storm

3. Increases in strength, adds moisture, clouds, and wind (Tropical Storm)

Hurricane Formation continued

4. Gets stronger – adds moisture, clouds, and wind – as long as it is over warm water (Hurricane)

5. When they move over cold water or land they lose energy

Hurricane Video # 1 Hurricane Video # 2

Storm Surge

• Storm Surge- A rise in sea level that happens during a storm.

Hurricane Damage

A stormsurge from a hurricane

can be up to 8 m high

Hurricane Safety

•Evacuate

•Move into the interior room and stay away from windows

Tornado• rapidly whirling, funneled-shaped cloud

reaches down from a storm cloud to touch Earth’s surface

• Usually brief, 15 minutes or less• Wind speeds may reach 480 km/hr (230

mph)• Counterclockwise in both the Northern and

Southern Hemispheres

Tornadoes1. Cold dry air meets warm moist air and causes

wind to move in 2 directions (cold dry air meets warm moist air)

2. a layer of air in the middle to being to spin

3. The spinning column of air is turned to a vertical position by strong updrafts of air in the cloud.

4. The spinning column of air moves to the bottom of the cumulonimbus cloud and forms a funnel cloud.

5. The funnel cloud becomes a tornado when it touches ground.

Tornadoes Fewer than 1% of thunderstorms produce tornadoes

About 75% of the world’s tornadoes happen in the United States

Most happen in the spring and early summer

Most last for only a few minutes

Average wind speeds are between 120 km/h and 180 km/h

Tornado Video # 1 Tornado Video # 2

Tornado Alley

Where is Tornado Alley?? An area of the United States where tornadoes are most frequent

Between Rocky & Appalachian Mountains

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Why is Central United States considered Tornado Alley?90% of tornadoes hit this region of the US

Cold, dry air from Canada/Rocky Mountains meets warm, moist air from the Gulf of Mexico and hot, dry air from deserts

Tornado Alley

The core of Tornado Alley consists of: Texas Panhandle Oklahoma Kansas Nebraska South Dakota Colorado Eastern Plains Ohio Valley The southern Great Lakes The Tennessee Valley The lower Mississippi Valley

Tornado Alley

A map Tornado Alley outlined. This area has been defined as the area where there has been approximately at least one significant tornado per day, per decade.

Tornado Safety

•Listen for watches & warnings•Basement level, or to the middle room on ground floor•Stay away from windows•Lie in a ditch

Recap!!!Why do thunder and lightning usually

happen together?When lightning moves through the air, the air gets very hot and expands rapidly. This makes the air vibrate which releases energy in the form of sound waves, called thunder.Where do most tornadoes happen. Why?

90% of tornados occur in Tornado Alley. This is a result of when the cold, dry air from Canada and the Rocky Mountains meets warm, moist air from the Gulf of Mexico and hot, dry air from deserts, which combines with atmospheric instability to produce intense tornadoes.

What type of energy powers hurricanes? How do hurricanes lose energy?

They are powered by solar energy. The sun’s energy causes ocean water to evaporate. When they move over cold water or land they lose energy.

Recap!!!

1) warm, moist air near Earth’s surface

2) an unstable area of the atmosphere

Which two conditions are required for thunderstorms to form:

A storm surge is a rise in sea level that happens during a storm. A hurricane can cause a storm surge to be 8 m high.

What is a storm surge? Which type of severe storm is most commonly associated with this?