Tornados
General Info
Generated in regions of already severe thunderstorms
Two prime factors for tornado initiation
The general topography
The local climate
Created over areas where air is undisturbed by mountains
Very common in midwest US
Known as tornado alley (tx, ok, ks, nb, ia, mo, il)
Most rare in alaska, texas has the most
Average by area though is florida
Is tornado alley changing with the changing climate
Gradually shifting eastward
Tornado Formation
Average dimensions
Width: 75 yrds
Track length: 1-4 miles (how long its on the ground)
Time on ground: 5 minutes
Forward speed: 25 mph
Timing
Prime season for the combination of ideal conditions
Spring to early summer
Although this appears to be shifting earlier
Prime time of day
Late afternoon to late evening
Time of maximum local ground and atmosphseric heating
The hottest part of the day
Tornado structure
Combinations of opposing wind patterns
High level, relatively dry/cooler winds from the west
Lower level, warm/wet winds from the southeast originating in the golf of mexico
Windows from cyclonic rotation parallel to the ground (called rollers)
Large thunderstorms pull warmer air upward from low levels
warm/wet air provides energy for the storm
Formation
Large updrafts can cause a roller to tip into a vertical position
Tornado is born upon touchdown with the ground
Large storms can produce more than one tornado
Called tornado families or storms
Ex - large tornado swarm in 1974 caused damage to 13 states from AL to OH
148 tornados touched down in about 16 hours
307 killed
Severe pressure drops (measured on a barometer)
Inside a twister can be as low as 3” mercury
For comparison
Average daily pressure her is 31-32”
Movement
Track direction is generally SW to NE
Combination of the prevailing wind direction from the west
The CCW rotation of the tornado
Fujita scale
Varies from EF0 to EF5
EF0 - weakest, with winds of 65-85 mph and minor damage to building/trees
EF5 - strongest with winds of >200 mph and complete destruction
Precise wind speed numbers are actually estimates based on damage after the storm and not measured directly during
EF0 = light damage some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged
EF1 = Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads
EF2 = Considerable damage. Roofs torn off frame houses; mobile homes demolished; train cars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground
EF3 = Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.
EF4 = Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.
EF5 = Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds.); trees debarked
Monitoring
Early 1980s
Device called TOTO
Designed to get swept up into a tornado and measure all the atmospheric parameters of a tornado from the inside
Scientists had to race to get ahead of a tornado and place the 400 pound cylinder squarely in its path
Never actually worked
Storm prediction center
Located in norman OK
Monitors regional weather conditions every morning
Issues a risk warning for severe weather later that day
Interacts with national weather service
National severe storms lab
Use of doppler radar
Measures the frequency change of objects moving away from the antenna
Interpets mesocyclones
Mobile doppler radar
Operated on a mobile platform to image nearby tornadic activity
Can get much closer to the tornado to image it more clearly
Mitigation
No practical efforts
Most injuries/death occur from flying objects or being picked up and thrown around
Scientific instrumentation and early warning systems are being improved
Detection lead times are only a matter of minutes to no more than an house
Very localized tracking by local tv
Safe rooms lined with concrete
Tornados
General Info
Generated in regions of already severe thunderstorms
Two prime factors for tornado initiation
The general topography
The local climate
Created over areas where air is undisturbed by mountains
Very common in midwest US
Known as tornado alley (tx, ok, ks, nb, ia, mo, il)
Most rare in alaska, texas has the most
Average by area though is florida
Is tornado alley changing with the changing climate
Gradually shifting eastward
Tornado Formation
Average dimensions
Width: 75 yrds
Track length: 1-4 miles (how long its on the ground)
Time on ground: 5 minutes
Forward speed: 25 mph
Timing
Prime season for the combination of ideal conditions
Spring to early summer
Although this appears to be shifting earlier
Prime time of day
Late afternoon to late evening
Time of maximum local ground and atmosphseric heating
The hottest part of the day
Tornado structure
Combinations of opposing wind patterns
High level, relatively dry/cooler winds from the west
Lower level, warm/wet winds from the southeast originating in the golf of mexico
Windows from cyclonic rotation parallel to the ground (called rollers)
Large thunderstorms pull warmer air upward from low levels
warm/wet air provides energy for the storm
Formation
Large updrafts can cause a roller to tip into a vertical position
Tornado is born upon touchdown with the ground
Large storms can produce more than one tornado
Called tornado families or storms
Ex - large tornado swarm in 1974 caused damage to 13 states from AL to OH
148 tornados touched down in about 16 hours
307 killed
Severe pressure drops (measured on a barometer)
Inside a twister can be as low as 3” mercury
For comparison
Average daily pressure her is 31-32”
Movement
Track direction is generally SW to NE
Combination of the prevailing wind direction from the west
The CCW rotation of the tornado
Fujita scale
Varies from EF0 to EF5
EF0 - weakest, with winds of 65-85 mph and minor damage to building/trees
EF5 - strongest with winds of >200 mph and complete destruction
Precise wind speed numbers are actually estimates based on damage after the storm and not measured directly during
EF0 = light damage some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged
EF1 = Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads
EF2 = Considerable damage. Roofs torn off frame houses; mobile homes demolished; train cars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground
EF3 = Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.
EF4 = Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.
EF5 = Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds.); trees debarked
Monitoring
Early 1980s
Device called TOTO
Designed to get swept up into a tornado and measure all the atmospheric parameters of a tornado from the inside
Scientists had to race to get ahead of a tornado and place the 400 pound cylinder squarely in its path
Never actually worked
Storm prediction center
Located in norman OK
Monitors regional weather conditions every morning
Issues a risk warning for severe weather later that day
Interacts with national weather service
National severe storms lab
Use of doppler radar
Measures the frequency change of objects moving away from the antenna
Interpets mesocyclones
Mobile doppler radar
Operated on a mobile platform to image nearby tornadic activity
Can get much closer to the tornado to image it more clearly
Mitigation
No practical efforts
Most injuries/death occur from flying objects or being picked up and thrown around
Scientific instrumentation and early warning systems are being improved
Detection lead times are only a matter of minutes to no more than an house
Very localized tracking by local tv
Safe rooms lined with concrete