This document discusses thunderstorms, tornadoes, and hurricanes. It describes the different types of thunderstorms like air-mass thunderstorms and severe thunderstorms including supercell thunderstorms. Tornado formation and occurrence are explained detailing how mesocyclones form and funnel clouds develop. Hurricanes are introduced covering their profile, formation from tropical disturbances, and decay when they move over land or cooler waters.

1. +
Thunderstorms, Tornadoes, Hurricanes
OH MY!!
Chapters 10 and 11

2. +
Thunderstorms
Sections 10.1 to 10.6

3. +
What’s in a Name?
Cyclone refers to the circulation around a
low-pressure center.
 Hurricanes
 Midlatitude cyclones
 Tornadoes

4. +
Thunderstorms
 Thunderstorms generate lightning, thunder, winds,
and hail.
 There are two types of thunderstorms.
 Air-mass thunderstorms are associated with warm,
humid air that rises in unstable environments;
cumulonimbus clouds, and mT (maritime tropical) air
masses.
 Severe thunderstorms may produce high winds, hail,
flash floods, and tornadoes.
 They are the result of uneven heating, frontal lifting,
and diverging winds.

5. +
Air-Mass Thunderstorms
Air-mass thunderstorms—mT air masses

6. +
Air-Mass Thunderstorms
Cumulus stage:
 Warm, humid air rises creating clouds that won’t
evaporate.
 A cumulonimbus tower develops as water vapor
moves from the surface to greater heights.
 Clouds pass freezing zone and Bergeron process
starts.
 Rain accumulation is too great for updraft so it falls
creating a downdraft via entrainment (influx of cool
dry air. Remember cold air gets heavy and sinks).

7. +
Air-Mass Thunderstorms
Mature stage:
 Thisis the most intense phase.
 This results in heavy rain and possibly
small hail.
 Cool downdrafts exist next to updrafts.
Dissipating stage:
 Thisstage is dominated by downdrafts and
entrainment causing evaporation.

8. +
Air-Mass Thunderstorms

9. +
Air-Mass Thunderstorms
Occurrence:
 Mountainous regions, such as the Rockies and
the Appalachians, experience a greater number
of air-mass thunderstorms.

10. +
Severe Thunderstorms
Severe thunderstorms:
 Heavy downpours
 Flash flooding
 Straight line wind gusts
 Hail, lightning
 Wind shear- change in wind speed or direction at
different heights
 Can overshoot (enter stratosphere)
 Downdraft preceding (gust front)

11. +
Supercell Thunderstorms

12. +
Supercell Thunderstorms
 Supercells
 These storms can produce extremely dangerous
weather.
 They consist of a single, powerful cell that can
extend to heights of 20 km or more.
 The clouds can measure 20–50 km in diameter.
 Mesocyclone:
 Verticalwinds may cause the updraft to rotate, which
forms a column of cyclonically rotating air.
 Tornadoes often form.

13. +
Supercell Thunderstorms
Squall lines:
 Squall lines are narrow bands of thunderstorms.
 cT (continental tropical) air is pulled into the
warm sector of a midlatitude cyclone.
 Mammatus skies sometimes precede squall
lines. (dark cloud rolls that have downward
pouches)
 These can also form along a dryline, where
there is an abrupt change in moisture.

14. +
Supercell Thunderstorms
Squall lines

15. +
Lightning and Thunder
 Lightning strokes:
 The flash (total discharge) lasts a few tenths of a
second.
 It is what we see and it contains multiple strokes.
 The leader is the ionized air, which forms a
conductive path.
 A step leader extends earthward in a short, nearly
invisible burst.
 The return stroke extends upward from ground to
cloud.

16. +
Lightning and Thunder
Thunder:
 The air is heated quickly to as much as
33,000°C.
 It expands explosively, which produces sound
waves that travels at 330 mps.
 If lightning is more than 20 km away,
thunder is not heard.

17. +
Lightning and Thunder
What causes lightning?

18. +
Tornadoes
Section 10.7 to 10.10

19. +
Tornadoes
Tornadoes (twisters, cyclones):
 These are violent windstorms with a rapidly
rotating column of air, or vortex.
 Pressures within tornadoes can be as much
as 10% lower than immediately outside the
storm.
 It may consist of single or multiple vortices.

20. +
Tornadoes

21. + The Development and Occurrence
of Tornadoes

22. +
The Development and Occurrence
of Tornadoes
Mesocyclones form
 Winds are stronger aloft producing rolling
motion about a horizontal axis
 Stronger thunderstorm updrafts tilt the
horizontal rotating air to a nearly vertical
alignment

23. +
The Development and Occurrence
of Tornadoes
The mesocyclone, vertical cylinder of air, is
established. It stretches vertically and
narrows horizontally causing wind speeds
to accelerate inward creating a vortex.
 FunnelCloud- vortex emerges from cloud
 Tornado- vortex touches the ground

24. +
The Development and Occurrence
of Tornadoes
Profile of a tornado:
 Average diameter 150–600m
 Travels ~45 kph
 Path about 26 km long
 Most travel to the NE
 Exist between <3 min to >3 hours
 Wind speeds between <150 kph to >500 kph
 Between 90- 300mph

25. +
Tornado Destruction

26. +
Hurricanes
Chapter 11

27. +
Profile of a Hurricane
 Hurricanes:
 Hurricanes are intense centers of low pressure.
 They form over tropical/subtropical oceans.
 These storms have intense convective activity and rotary
circulation and can have wind speeds in excess of 74mph.
 They are usually 100–1500 km in diameter, form between
5° and 20° latitude and have a steep pressure gradient.
 Hurricanes are called typhoons in the NW Pacific and
cyclones in the SW Pacific and Indian Oceans.

28. +
Profile of a
Hurricane
Eye wall: doughnut
shaped wall of
intense convective
activity surrounding
the eye.
Eye: Center of
hurricane where wind
and rain cease

29. +
Hurricane Formation and Decay
Hurricanes:
 Hurricanes are fueled by the latent heat of
condensed water vapor.
 Most are formed from late summer to early fall.
 Sea-surface temperatures of 27°C or higher
provide the necessary heat and moisture.

30. +
Hurricane Formation and Decay
Hurricane formation:
 Tropical disturbances,
such as disorganized
cloud arrays and
thunderstorms,
occasionally grow
larger and develop
strong cyclonic rotation.
 Easterly waves
gradually move from
east to west.

31. +
Hurricane Formation and Decay
 Hurricane formation:
 As areas within tropical disturbances get warmer, several
factors help form hurricanes.
 Surface pressure drops creating a region of weak low
pressure and cyclonic circulation.
 Higher pressure develops at the top of the storm causing
an outward flow of air from the top.
 If wind speeds do not reach 63 kph, it is called a tropical
depression.
 When winds exceed 61 kph, it becomes a tropical storm
and is given a name.

32. +
Hurricane Formation and Decay
Hurricane decay:
 Decay occurs when latent heat is cut off.
 A hurricane moves over cooler water or land.
 When large scale flow aloft is unfavorable, they
diminish in intensity.