2. Cloud Formation
 All types of cloud formation depend on water vapour
condensing in the air
 Condensation occurs when the air cannot hold as
much water as it has dissolved in it
 Most common reason for condensation is temperature
 Hot- holds lots of water
 Cold- hold very little water

3. Continued
 In order to form clouds we need condensation in the
atmosphere. This can happen in a number of ways:
 Convection clouds
 Frontal clouds
 Orthographic clouds
 Fog

4. Convection Clouds
 The sun heats the ground
 Hot air rises
 Air cools and condenses
 Why does air cool?
 Warm air rises, less pressure up high, less pressure =
expansion = cooling

5. Frontal Clouds
 Fronts are regions of air with the same general
properties
 Cold: low temperature, high pressure, and low
humidity
 Hot: high temperature, low pressure, and high
humidity
 On a front line two different air masses interact
creating clouds. As the two air masses interact the
warm front moves over the cold front.

6. Orthographic Clouds
 Works the same way as frontal clouds, but instead of a
cold front forcing the warm air mass up, a geographic
feature does.
 Ex. Moist air moves over Vancouver to the base of the
Rockies. The warm moist air rises and cools at the top
of the mountain. The water vapour condenses and
falls as rain or snow on the side of the mountain. The
warm, dry air continues down the other side of the
mountain, often is called a chinook.

7. Fog
 Is a cloud that forms near the ground
 Can be caused multiple ways:
 Cool ground cools the air and condenses the water
vapour into clouds
 Warm air drifts over snow covered ground and
condenses
 Moist air drifts over a cold current

8. Classifying Clouds
 There are two main shapes of clouds
 Cumulus- billowing, rounded shapes
 Stratus- flattened, layered shapes
 There are ten main clouds:
 Cirrus- thin, wispy clouds made of ice crystals ( below
8000m)
 Cirrocumulus- thin, patchy clouds that form wavy
patterns ( 6000m to 8000m)

9. Continued
 Cirrostratus- thin veiled clouds (6000m to 8000m)
 Cumulonimbus- large, darker clouds (8000m to 15000m)
 Altostratus- sheets of grey or blue (3000m to 7000m)
 Altocumulus- grey or white puffy clouds (3000m to
7000m)
 Stratocumulus- irregular rolling or puffy clouds (2000m)
 Cumulus- low, rounded clouds (below 2000m)
 Nimbostratus- rain clouds, dark wet looking (below
2000m)
 Stratus- low, uniform sheet clouds (below 2000m)

10. Regional Weather
 There are five main types of regional weather:
thermals, sea breezes, land breezes, lake-effect snow,
and Chinook winds
 Thermals- solar energy heats up the land, the energy is
converted to heat and warms the air it comes in
contact with
 Warm air expands and becomes less dense
 The less dense air rises and is replaced by cooler,
denser air, setting up a convection current
 A local convection current set up during the day is
called a thermal of a thermal updraft

11. Continued
 Sea breezes- when a thermal forms near a body of
water it is called a sea breeze
 Land warms faster than water
 The convection current moves the air from the water to
the land
 Land Breezes- land cools down faster than water
 The air above the water rises and is replaced by cooler
air from above the land
 This causes a land breeze, a convection thermal that
flows form land to water

12. Continued
 Lake effect snow- moisture laden air rises and moves across
a body of water and reaches the far side of the body of
water
 The temperature of the land is cooler so the moisture
becomes snow
 Chinook winds- on the windward side of the mountains,
orographic lift causes water vapour to condense and make
clouds and snow or rain
 Condensing water vapour releases energy, warming the air
 The air that sinks on the leeward side of the mountain is
dry but gained some heat
 The resulting warm dry air is called a chinook

13. Weather Systems
 Air masses have the properties of the surface that they
originate over
 Form over water = humid (maritime)
 Form over land = dry (continental)
 Form in the south = warm (tropical)
 Form in the north = cold (polar)
 Ex. Colorado Lows: maritime tropical
 Bring in most of the blizzard in Manitoba

14. Thunderstorms
 Most often caused by convection clouds, usually paired
with a frontal system
 The one thing it needs is rapidly rising air
 Ex. Sun heats ground, air continues to rise “pushing” cloud
up. Makes a anvil shaped cumulonimbus cloud, top is
flattened by jet stream
 Rising and falling air rub against each other, friction creates
large static charge, or in other words, lightning
 Sheet lightning is the positive and negative charges in the
cloud “jumping” to one another
 Fork lightning is the negative charge of the base of the
cloud “jumping” to the positive ground

15. Hail
 Rain falls and the wind blows it back up
 The rain freezes and falls
 Ice gathers more water and is blown back up
 The cycle continues until the ice is too heavy
 Ice falls to earth as hail, the stronger the wind, the
larger the hail

16. Tornados
 When the updrafts are strong enough tornados develop
 Anytime there is a severe storm it carries the risk of a
tornado
 If hail forms, it sometimes is a precursor to a tornado
 When the updrafts are strong enough the air begins to
swirl
 When the swirling winds develops in the clouds it does not
“touch down” on its own
 When conditions are “right” a large sudden down pour
causes a rear flanking down draft
 This down draft causes the fennel down to a “touch down”

17. Continued
Scale Winds (km/h) Length of path Width Damage
(km)
0 (very weak) Under 116 Under 1.5 Under 15m Minor roof, tree,
chimney, antenna,
and sign damage
1 (weak) 117-180 1.6-5 50m Barns torn apart,
trees snapped
2 (Strong) 181-252 5.1-15.9 160m Roofs torn off
buildings, trees
uprooted
3 (severe) 253-332 16-50 61-500m Weaker homes
completely
disappear
4(devastating) 333-419 51-159 0.5-1.4 km Cars thrown, walls
of homes blown
apart
5 (incredible) 420-512 160-507 1.5-16 km Strongly built
homes completely
blown away

18. Hurricanes (Cyclogenesis)
 Northern Hemisphere: hurricane
 Southern Hemisphere: hyphoon
 Storm develops in Africa
 Warm water feeds the storm
 Hits land and dissipates quickly
 The circular shape I caused by the coriolis effect
 Warm air rises and circles in rings, causing very low
pressure
 The eye is the center, it has extremely low pressure

19. Continued
 The pressure isn’t enough to pick you up but is low
enough to raise there ocean level
 This along with waves is the “storm surge” and is the
most damaging part of the storm
 The water level rises between 1 and 6m
 If this happens at a high tide dyke or a levee, they are
often breached

20. Continued
Category Max surface Min surface Storm surge Remarks
pressure pressure (m)
(km/h) (kPa)
1 (minimal) 119-153 98.0 or more 1.0-1.7 Damage to trees
and signs,
flooding in low-
lying areas
2 (moderate) 154-177 97.9-96.5 1.8-2.6 Trees blown down,
evacuation of
shore areas
3 (extensive) 178-209 96.4-94.5 2.7-3.8 Serious coastal
flooding, mobile
homes destroyed
4 (extreme) 210-249 94.4-92.0 3.9-5.6 Extensive damage
to buildings,
evacuation from
shore required
5 (catastrophic) Above 250 Under 92.0 Above 5.6 Buildings
destroyed,
evacuation up to
20km inland
required