thunderstorms, tornadoes, hurricanes oh my!
TRANSCRIPT
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Thunderstorms, Tornadoes, Hurricanes OH MY!!
Chapters 10 and 11
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Thunderstorms
Sections 10.1 to 10.6
+What’s in a Name?
Cyclone refers to the circulation around a low-pressure center.HurricanesMidlatitude cyclonesTornadoes
+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.
+Air-Mass Thunderstorms
Air-mass thunderstorms—mT air masses
+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).
+Air-Mass Thunderstorms
Mature stage: This is the most intense phase.
This results in heavy rain and possibly small hail.
Cool downdrafts exist next to updrafts.
Dissipating stage:This stage is dominated by downdrafts and
entrainment causing evaporation.
+Air-Mass Thunderstorms
+Air-Mass Thunderstorms
Occurrence:Mountainous regions, such as the Rockies and
the Appalachians, experience a greater number of air-mass thunderstorms.
+Severe Thunderstorms
Severe thunderstorms:Heavy downpoursFlash floodingStraight line wind gustsHail, lightningWind shear- change in wind speed or direction at
different heightsCan overshoot (enter stratosphere)Downdraft preceding (gust front)
+Supercell Thunderstorms
+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:Vertical winds may cause the updraft to rotate, which
forms a column of cyclonically rotating air.Tornadoes often form.
+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.
+Supercell Thunderstorms
Squall lines
+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.
+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.
+Lightning and Thunder
What causes lightning?
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Tornadoes
Section 10.7 to 10.10
+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.
+Tornadoes
+ The Development and Occurrence of Tornadoes
+The Development and Occurrence of Tornadoes
Mesocyclones formWinds are stronger aloft producing rolling
motion about a horizontal axisStronger thunderstorm updrafts tilt the
horizontal rotating air to a nearly vertical alignment
+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.Funnel Cloud- vortex emerges from cloudTornado- vortex touches the ground
+The Development and Occurrence of Tornadoes
Profile of a tornado:Average diameter 150–600mTravels ~45 kphPath about 26 km longMost travel to the NEExist between <3 min to >3 hoursWind speeds between <150 kph to >500 kph
Between 90- 300mph
+Tornado Destruction
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Hurricanes
Chapter 11
+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.
+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
+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.
+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.
+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.
+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.