Download Severe Weather Notes

TORNADOES
 are a low pressure storm that usually forms over land
 in an average year, 800 tornadoes are reported in the U.S.
 a tornado is defined as a violently rotating column of air
extending from a thunderstorm to the ground…the rotating
column of air is called the vortex
 the vortex is only visible when debris and dirt gets carried up
with the winds
Where do they come from?
 Tornadoes come from the energy released in a
thunderstorm.
 What makes them dangerous (as compared to hurricanes)
is that their energy is concentrated in a small area, only a
hundred yards across.
When & Where do they occur?
 Most common east of the Rocky Mountains and west of the Appalachian Mountains.
 They occur mostly during the spring and summer (April-June)
 They usually occur during the late afternoon and early evening.
 Usually happen along cold fronts
How long is a tornado usually on the ground?
 Can range from a few seconds to several hours ... 5 minutes is average
How fast do tornadoes move?
 Movement can range from virtually stationary to more than 60 miles per hour ... average
is 10-20 miles per hour.
Do you know the difference?
Watch—means conditions are favorable for tornado to develop
Warning—means that a tornado has been spotted
MEASURING DESTRUCTION
The Enhanced Fujita Scale rates tornadoes based on the amount and
type of wind damage produced.
The Enhanced Fujita (EF) Scale
EF-0. Light damage
Wind 65 to 85 mph. Causes some damage to siding and shingles
EF-1. Moderate damage
Wind 86 to 110 mph. Considerable roof damage. Winds can uproot
trees and overturn single-wide mobile homes. Flagpoles bend.
EF-2. Considerable damage
Wind 111 to 135 mph. Most single-wide mobile homes destroyed.
Permanent homes can shift off foundation. Flagpoles collapse.
Softwood trees debarked.
EF-3. Severe damage
Wind 136 to 165 mph. Hardwood trees debarked. All but small portions of houses destroyed.
EF-4. Devastating damage
Wind 166 to 200 mph. Complete destruction of well-built residences, large sections of school
buildings.
EF-5. Incredible damage
Wind above 200 mph. Significant structural deformation of mid- and high-rise buildings.
HURRICANES
 Low pressure systems that form over warm, tropical waters near the equator
 Most form between 5 and 20 degrees north latitude—they almost never form in the South
Atlantic
 Different names are given to hurricanes depending on
where they form
1. Atlantic—we call them hurricanes
2. Pacific—they are called typhoons
3. Indian Ocean—they are called cyclones
 Mature hurricanes average about 350 miles across
 They have the lowest barometric pressures ever recorded
with any storm (905 millibars is lowest recorded)
 These huge air pressure differences is what creates the rapid, inward spiraling of winds
HURRICANE DEVELOPMENT
 When winds have developed speeds from 39 to 73 miles per hour, it is called a tropical
storm (storms are given names when they begin to have winds of this speed).
 The storm becomes a hurricane when it reaches a wind speed of 74 mph
 When a season is very active, Greek letters are used to name tropical storms after the
letters of the alphabet had been used.
END OF A HURRICANE
When a hurricane travels over land or cold water, its energy source
Retired Replacement
(warm water) is gone and the storm weakens, quickly dying.
Name Name
Allison Andrea
HURRICANE SEASON
Floyd Franklin
Georges Gaston
 Occurs from June through November
Iris
Ingrid
 Most hurricanes form during the late summer months because the
Katrina Katia
ocean is still retaining heat from the warmer earlier months
Keith Kirk
MEASURING DESTRUCTION
Lenny Lee
We use the Saffir-Simpson scale to rank hurricane intensities
MichelleMelissa
Saffir-Simpson Scale
CATEGORY
1
2
3
4
5
WIND SPEED
74-95 mph
96-110 mph
111-130 mph
131-155 mph
Greater than 155
STORM SURGE
4-5 feet
6-8 feet
9-12 feet
13-18
Greater than 18
DAMAGE
Minimal
Moderate
Extensive
Extreme
Catastrophic
STORM SURGE ACCOUNTS FOR 90% OF
HURRICANE-CAUSED DEATHS
AMAZING EARTH SCIENCE FACTS
 High pressure systems move clockwise and
outward
 Low pressure systems move
counterclockwise and inward.