Transcript Ch 13 sections 2 and 3 - OG

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.
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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
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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 temp
if 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 (draw)
(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
* 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, lightning, 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

Lightning 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. charges 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
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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 > 119 km/hr = hurricane.

Eye – center w/ clear skies and light wind.
Eyewall
Rainbands
P. 466

Pictures of damage?
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Blizzards: conditions must be
1. Winds 56 km/h
 2. Temp is LOW
 3. Visibility is less than 400 m. in falling or
snow.
1. blowing
Winds 56
km/h
 4.
Conditions
2.
Temp
is LOWpersist for 3 hours or more.

3. Visibility is less than 400 m. in falling or
blowing snow.
4. Conditions persist for 3 hours or more.
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
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
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Cloud Cover

Temperature

Dew Point

Wind Speed and direction
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Previous weather
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Current weather

Pressure change
 What’s this tell you?
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Read Chapter if you haven’t.
Make your note cards or foldables.
Study them every night from now until the
test.