Transcript Chapter 13 Notes

Chapter 13
The Nature of Storms
Thunderstorms
• Three conditions required:
– Source of moisture
– Rising air mass
– Unstable atmosphere
• Air mass t-storms
T-storm days per year
– Orographic (mountain)
– Sea breeze
– Convection
• Frontal t-storms
– Advancing cold fronts (squall
line)
Sea breeze
Three Stages of Thunderstorm
Development
Lightning and Thunder
• Transfer of electricity (similar to static electric
shock)
• 5 times hotter than the sun’s surface
• Thunder is the sonic boom made by
expanding air
• Forest fires, injuries, and deaths
• Lightning causes more annual deaths (on
average) than tornadoes, hurricanes or floods
Lightning Strikes
Supercells
• Severe t-storm
• Fastest winds
on Earth
• Can last for
several hours
• Strong winds
• Hail
• Downbursts
• Tornadoes
There are about 100,000 thunderstorms in the United
States each year. About 10% of those are severe; fewer
still are supercells.
Tornado Development
• Horizontal
rotating air is
lifted vertically
by t-storm
updraft
• 80% of all
tornadoes are
weak (F0 or F1)
Tornado Classification
Tornado Frequency Map
• “Tornado alley”—Texas,
Oklahoma, Kansas,
Missouri
• Most common in
spring during late
afternoon and
evening
• Only about 1% of all
tornadoes are violent
(F4 or F5)
• Safety: Shelter in a
basement or interior
room; NOT in a car or
mobile home
Hurricanes/Tropical Storms
• Begin to form over
warm tropical oceans
• Air rises and pulls in
more warm humid air
• Coriolis effect causes
cyclonic rotation
• Wind speeds are used
to classify tropical
storms/hurricanes
Floods and Droughts
• Floods and flash floods can occur after storms
or a hurricane moves through an area
• Coastlines, floodplains, and narrow river
valleys are most susceptible
• Drought—extremely dry weather—can also
cause damage
• Droughts are usually caused by sustained high
pressure systems
Heat Waves/Cold Waves
• Heat waves are often produced by high
pressure systems that cause droughts
• High humidity adds to the discomfort of high
temperatures (see next slide)
• Cold waves are also produced by large high
pressure systems
• Windchill magnifies the effect of cold weather
for people
Heat Index