section 2 and 3 weather patterns air pressure = weight of the molecules in a large mass of air. (2...

Section 2 and 3 Weather Patterns

Air pressure = weight of the molecules in a large mass of air. (2 TYPES) ◦1) HIGH pressure system Cool air masses More “weight” because cool =>

molecules are closer together. (Sinking air at center.)

Air moves clockwise – away from center. Associated w/ clear skies and fair

weather.

2) Low Pressure System◦Warm air masses.◦Less dense => air molecules are farther

apart.◦Air moves counter clockwise – towards

the center.◦Air rises at center which then cools and

water vapor condenses.◦Associated w/ cloudy weather and

sometimes precip. *Know how to compare and contrast the two!!!

Winds blow from HIGH to LOW (areas of air pressure).

Air Mass: large body of air that has uniform temp., humidity, and pressure. Takes on the temp, etc. of the surface where it formed.

Ex. Air mass over tropics will be warmer than an air mass that develops over the North Pole.

Ex. Air mass that develops over land is dryer than an air mass that develops over water.

1) Arctic Air Masses = bitterly cold, dry air.◦ Form Siberia & Arctic – kind that causes neg.

temps. 2) Continental Polar Air Masses = fast

moving, cold & dry.◦ Cold temps in winter & cool weather in summer.

3) Maritime Polar Air Masses = cold & humid.◦ Bring cloudy, rainy weather.

4) Continental Tropical Air Masses = hot & dry.◦ Bring clear skies and high temps.

5) Maritime Tropical Air Masses = Hot & humid. Summer – hot & humid

Winter – heavy snowfall

Change as they move from land to ocean and from ocean to land.

Remember: if over land (“continental”) = dry

if over ocean (“maritime”) = moisture

if POLAR = cold tempif TROPICAL = warm temp

FRONTS•Definition: Boundary between 2 air masses of different density, moisture, or temp.

•4 kinds!!! Pictures on P. 462 – 463

•1.) Cold Front: •cold air advances toward warm air.•Cold air wedges under warm air.

(think snow plow)•Represented by blue lines w/ triangles on weather map(When temp diff is large, thunderstorms or tornados can form.)*Brings drop in temp, clouds, precip, wind & severe storms

•2.)Warm Front: •Form when lighter, warmer air advances over heavier, colder air.

•Represented by red lines w/ semicircles on weather map.

* Brings rising temps, steady rain & a change in wind direction.

3.)Occluded Front

*Need 3 air masses.*Usually 2 cold fronts close off a warm front from the surface.*Usually precip

4.)Stationary Front•Boundary between air masses stops advancing. (They are stuck – days of precip.)•Represented by alternating blue and red lines w/ triangles and semicircles.

Thunderstorms: ◦Heavy rains, lightening, thunder, hail, etc.◦Occur in Warm, moist, air masses and

along fronts (boundaries!!!)◦Sinking, rain cooled air and strong updrafts

of warmer air cause the strong winds.◦To be “severe” – winds 89 m/hr or more.◦Damage: Flash Floods – happen w/out warning Hail and / or Wind Damage Lightening strikes

◦Sinking, rain cooled air and strong updrafts of warmer air Cause clouds to become charged. Forms a current between these charged clouds and ground or object

Pos. and Neg. join …. Makes the flash.

Results from: ◦the rapid heating of air around the lightning

◦ then it rapidly cools and contracts.

Makes a sound wave = thunder

1.)Tornado: ◦Produced by thunderstorms◦Whirling, violent wind that moves over narrow strip of land

◦Funnel Cloud – in air◦Tornado – called this when it touches ground!!

◦Fujita Classification F1 – F4 moderate damage, F5 incredible damage!

2.)Hurricanes: (150,000 x larger than tornado)*The most POWERFUL storm.*Large, swirling low-pressure formed over the Atlantic Ocean (Called Typhoons in Pacific Ocean and Cyclones in Indian Ocean.)*Must have at least 119 km/hr.*As long as it is over water, gains strength and continues …

– water provides energy for storm – once it hits land, its source of energy

disappears

1) Low pressure system over ocean. 2) Tropical Depression forms =

thunderstorms w/ winds bt. 37 – 62 km/hr. 3) Tropical Storm – air continues to rise …

winds > 63 km/hr, thunderstorms 4) Winds > 116 km/hr = hurricane.

Eye – center w/ clear skies and light wind. Eyewall Rainbands P. 466

Pictures of damage?

1. Winds 56 km/h 2. Temp is LOW 3. Visibility is less than 400 m. in falling or

blowing snow. 4. Conditions persist for 3 hours or more.

Blizzards: conditions must be

1. Winds 56 km/h2. Temp is LOW3. Visibility is less than 400 m. in falling or blowing snow.4. Conditions persist for 3 hours or more.

WATCHES: issued when conditions are favorable for severe weather like tornadoes, thunderstorms, winter storms …

WARNINGS: severe weather conditions already exist (may be moving into our area)

P. 468 (1-8)

Next up … reading Weather Maps

–Meteorologists:

• person who studies the weather.• Takes/uses measurements of temperature, air pressure, winds, humidity, and precipitation to:–Used to make weather maps–The maps allow them to make predictions about future weather patterns.

1) Surface Report◦Def: describes a set of weather measurements made on Earth’s surface.

◦Weather Stations – instruments that report:

◦ temp, air pressure, humidity, precip, & wind direction/speed. (weather VARIABLES)

2) Upper-air Report◦Def: describes wind, temp, & humidity conditions ABOVE Earth’s surface.

◦Measured by a RADIOSONDE (carries weather instruments)

◦Many km high in atmosphere in a weather balloon.

◦pictures of weather balloon

3) Satellite / Radar Images◦Infrared Images How much thermal energy stored is in

atmosphere. Cloud height Atmospheric temps

◦Doppler Radar – Detects precipitation Movement of small particles (used to

approximate wind speed) Important tool during severe storms

Data gathered at Earth’s surface Used to make a map w/ symbols called

Station Model This info entered into computer w/ the data

collected from atmosphere - used to make forecasts (what is coming or happening to the weather)

Isobars – line that connects areas of equal atmospheric pressure.◦ Help indicate where areas of High and Low-

pressures are …◦ Lines closer together means stronger winds

… Isotherms – line that connects areas of

equal temperature.

P. SR – 46 Weather Map Symbols P. 473 Weather Map

Read Chapter if you haven’t. Make your note cards or foldables. Study them every night from now until the

test.