tornadoes the recent oklahoma experience
Skip this Video
Download Presentation
Tornadoes....The recent Oklahoma experience.

Loading in 2 Seconds...

play fullscreen
1 / 106

Tornadoes....The recent Oklahoma experience. - PowerPoint PPT Presentation

  • Uploaded on

Tornadoes....The recent Oklahoma experience. With a Tribute to Moore in May 99 Charles Stewart MD EMDM. Evolution of the tornado. Formation of a Thunderstorm.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'Tornadoes....The recent Oklahoma experience.' - quito

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
tornadoes the recent oklahoma experience
Tornadoes....The recent Oklahoma experience.
  • With a Tribute to Moore in May 99
  • Charles Stewart MD EMDM
formation of a thunderstorm
Formation of a Thunderstorm
  • When the ground warms and the high air is cold… the warm air near the surface rises. As it cools, the water vapor will condense, forming clouds
ordinary thunderstorms
Ordinary Thunderstorms
  • Three stages have been identified in ordinary thunderstorms:
  • an unstable atmosphere and vertical updrafts keep precipitation suspended
  • entrainment of dry air that causes cooler air from evaporation, triggering downdrafts and falling precipitation and gust fronts
  • weakening updrafts and loss of the fuel source after 15 to 30 minutes.
severe thunderstorms
Severe Thunderstorms
  • Severe thunderstorms produce a minimum of
    • 3/4 inch hail and/or
    • wind gusts of 50 knots and/or
    • tornado winds.
  • In ordinary storms, the downdraft and falling precipitation cut off the updraft.
  • In severe storms, winds aloft push the rain ahead and the updraft is not weakened and the storm can continue maturing.
  • The single supercell storm shown here maintained its structure for hours
multicell storms
Multicell Storms

Cool downdrafts leaving a mature and dissipating storm may offer relief from summer heat, but they may also force surrounding, low-level moist air upward.

Hence, dying storms often trigger new storms, and the successive stages may be viewed in the sky.

pre frontal squall lines
Pre-frontal Squall Lines

Pre-frontal squall lines identify major storms triggered by a cold front that may contain several severe thunderstorms, some possibly supercells, extending for more than 1000 kilometers.

This 1989 storm spawned 25 tornadoes, the worst killing 25 people.

mesoscal convective complex
Mesoscal Convective Complex

An organized collection of thunderstorms extending across a large region is a mesoscale convective complex (MCC).

MCC's can regenerate new storms and last for upwards of 12 hours and may bring hail, tornadoes, and flash floods.

They often form beneath a ridge of high pressure.

gust front and microburst
Gust front and Microburst
  • Turbulent air forms along the leading edge of the gust front, which can generate tumbling dust clouds.
  • Such gust fronts and associated cold dense air often feel like a passing cold front, and may cause a 1 to 3 mb local rise in pressure, called a mesohigh.
shelf cloud
Shelf Cloud
  • When unstable air is prevalent near the base of the thunderstorm, the warm rising air along the forward edge of the gust front is likely to generate a shelf, or arcus, cloud.
trailing stratified clouds
Trailing Stratified Clouds
  • An extensive region of stratified clouds may follow behind a squall line.
  • This figure shows a loop of rising and falling air that supplies the moisture to the stratiform clouds and associated light precipitation
wind shear formation
Wind Shear Formation
  • When winds aloft blow in one direction and winds on the surface blow in another direction, they create a horizontally rotating mass of air

This is wind shear formation --- the ‘roll cloud’.... more later.

dry line formation
Dry Line Formation

Abrupt geographic changes from moist to dry dew-point temperature, called drylines, form in western TX, OK, and KS in the spring and summer.

Cool air pushes hot and dry air over the warm moist air, at the height of the central plains. Such mixing causes large scale instabilities and the birth of many supercell storms.

thunderstorm movement
Thunderstorm Movement
  • Middle troposphere winds control individual thunderstorms.
  • Dying storm downdrafts spawn new storms so the storm system moves rightwards relative to the upper level winds.
  • Here upper level winds move storms to the northeast, but downdrafts generate new cells to the south, which eventually cuts off moisture to the old cell.
Lightning & Thunder

Charge differences between the thunderstorm and ground can cause lightning strokes of 30,000°C, and this rapid heating of air will creates an explosive shock wave called thunder, which requires approximately 3 seconds to travel 1 kilometer.

Lightning Stroke Development

Charge layers in the cloud are formed by the transfer of positive ions from warmer hailstones to colder ice crystals.

When the negative charge near the bottom of the cloud is large enough to overcome the air's resistance, a stepped leader forms.

A region of positive ions move from the ground toward this charge, which then forms a return stroke into the cloud.

Types of Lightning

Nearly 90% of lightning is the negative cloud-to-ground type, but positive cloud-to-ground lightning can generate more current and more damage.

Several names, such as forked, bead, ball, and sheet lightning describe forms of the flash.

Distant, unseen lightning is often called heat lightning.

Lightning Rods & Fulgurite

Metal rods that are grounded by wires provide a low resistance path for lightning into the earth, which is a poor conductor.

The fusion of sand particles into root like tubes, called fulgurite, may result.


A rapidly rotating column of air often evolves through a series of stages, from dust-whirl, to organizing and mature stages, and ending with the shrinking and decay stages.

Winds in this southern Illinois twister exceeded 150 knots.

Tornado Occurrence

Tornadoes from all 50 states of the U.S. add up to more than 1000 tornadoes annually, but the highest frequency is observed in tornado alley of the Central Plains.

Nearly 75% of tornadoes form from March to July, and are more likely when warm humid air is overlain by cooler dryer air to cause strong vertical lift.

the 4 new tornado alleys
The 4 “New Tornado Alleys”

Recent researchshows that there

are really 4 separate

tornado alleys…

Tornado alley

Hoosier alley

Dixie alley

Carolina alley

  • How we get from....
  • To here:
wind shear initiates rotation
Wind Shear initiates rotation...

Remember wind shear formation --- the ‘roll cloud’ -

The first sign that a supercell may form a tornado is rotating clouds at the base of the storm, which may lower and form a wall cloud, shown in this picture.
rotation moved from horizontal to vertical
Rotation Moved From Horizontal to Vertical

Spinning horizontal vortex tubes created by surface wind shear may be tilted and forced in a vertical path by updrafts. This rising, spinning, and often stretching rotating air may then turn into a tornado.

This changes the roll cloud into a vertical formation: A tornado

tornado wind speed
Tornado Wind Speed

As the tornado moves along a path, the circular tornado winds blowing opposite the path of movement will have less speed.

For example, if the storm rotational speed is 100 knots, and its path is 50 knots, it will have a maximum wind of 150 knots on its forward rotation side.

suction vortices
Suction Vortices...

A system of tornadoes with smaller whirls, or suction vortices, contained within the tornado is called a multi-vortex tornado.

Damage from tornadoes may include its low pressure centers causing buildings to explode out and the lifting of structures.

Human protection may be greatest in internal and basement rooms of a house.

tornado occurrence
Tornado Occurrence

Tornadoes from all 50 states of the U.S. add up to more than 1000 tornadoes annually, but the highest frequency is observed in tornado alley of the Central Plains.

Nearly 75% of tornadoes form from March to July, and are more likely when warm humid air is overlain by cooler dryer air to cause strong vertical lift.

tornado watch or warning
Tornado Watch... or Warning?

Tornado watches are issued = tornadoes are likely

Tornado warning = a tornado has been spotted.

Once the storm has passed, the magnitude of the storm is classified based on damage done by the storm. – This is the ENHANCED Fujita scale.

tornado breeding superstorms
Tornado Breeding Superstorms

Supercell thunderstorms may have many of the features illustrated here, including a mesocyclone of rotating winds formed when horizontal vorticity was tilted upwards.

rear flank downdraft
Rear Flank Downdraft

Supercell thunderstorm development may create an area where the updraft and counterclockwise swirl of upper winds converge into a rear flank downdraft.

This downdraft can then interact with lower level inflow winds and spawn a tornado.

non supercell tornadoes
Non-Supercell Tornadoes

If a pre-existing wall cloud was not present, than any tornado formed is not from a supercell storm.

These tornadoes are often not as strong as those formed by supercells.

doppler radar
A single Doppler radar unit can uncover many features of thunderstorm rotation and movement, but cannot detect winds parallel to the antenna.

As such, data from two or more units might be combined to provide a complete view of the storm.

Doppler lidar (light beam rather than microwave beam) provides more details on the storm features, and will help measure wind speeds in smaller tornadoes.

Doppler Radar
nexrad wind analysis
NEXRAD Wind Analysis
  • NEXt Generation Weather RADar (NEXRAD)
  • Uses Doppler measurements to detect winds
    • moving toward (green)
    • moving away (blue)
  • Which shows areas of rotation and strong shear.

Warm, shallow coastal water is often home to waterspouts, which are simply a tornado over water

The waterspout does not draw water into its core, but is a condensed cloud of vapor.

A waterspout may, however, lift swirling spray from the water as it touches the water surface.

comparing beaufort fujita and mach scales
Comparing Beaufort, Fujita, and Mach Scales

These scales have wind speed defined first, impacts/damage were assigned to wind speeds.




Beaufort: V = 1.870B3/2mph

F – scale: V = 14.1(F+2)3/2mph

Mach scale: V = (742 +1.3)Mmph





























Fujita Scale
















Mach Scale

Beaufort Scale

fujita tornado scale1
Fujita Tornado Scale

The Fujita scale is

designed to show the wind speed.

Damage assessment was derived after the fact… this led to a few problems.

the enhanced fujita scale
The Enhanced Fujita Scale

The Enhanced Fujita scale is a damage assessment scale that is related to wind speed.

Damage assessment drives the calculation and assignment of the ‘EF’ number.

ef has 28 damage indicators
EF has 28 Damage Indicators


Commercial/retail structures


Professional buildings

Metal buildings/canopies



each indicator has degrees of damage
Each indicator has “Degrees Of Damage”

Note some consecutive DODs have larger overlap than others

Example DODs for a Framed House DI (FR12 or DI2)

degrees of damage
“Degrees Of Damage”

Expected wind 97 mph

f to ef conversion
F to EF Conversion

Wind speeds in mph, 3-second gust

picher ok vital statistics
Picher, OKVital Statistics

Population (year 2000): 1,640.

Estimated population in July 2006: 1,633 (-0.4% change)

Males: 800 (48.8%)

Females: 840 (51.2%)

Ottawa County

Median resident age: 36.8 years

Oklahoma median age: 35.5 years

Zip codes: 74360.

Approximately 60% of houses are abandoned.

lone grove tornado1
Lone Grove Tornado
  • EF4 Tornado
    • First violent February tornado since 1950
    • Killed 8, Injured 46
  • Part of complex that hit OKC and Edmond
    • 6 reported tornadoes in OK that day.
degrees of damage1
“Degrees Of Damage”

All walls collapsedExpected wind 170 mph

frame house damage
Frame House Damage

An EF-4 tornado, with winds estimated by the National Weather Service at 180 mph to 185 mph

20 minutes vs 60 seconds
20 minutes vs 60 Seconds?
  • Data analysis of 18,000 tornadoes between 1986 and 2002.
  • On average advanced warning reduced expected injuries by about 32 percent.
  • Overall, when people were notified of a tornado up to about 15 minutes ahead of time, deaths decreased.

However, lead times greater than 15 minutes seemed to increase fatalities compared with no warning.

15 minute warning
> 15 Minute Warning

"There is anecdotal evidence that came out of the tornadoes in Oklahoma and Missouri in February. Out of the 23 fatalities, eight were people in cars. I don't know if those people were trying to outrun the storm, or if they just happened to be in their cars."

15 minute warning1
> 15 Minute Warning

When people don't know what to do in a dangerous situation, many times they do the wrong thing. I am surprised the authors didn't take that approach. It is almost like they are saying that advance warning is a bad thing, when in reality it is a GREAT thing; it's just that people are not well educated enough to know how to respond.


In the event our luck does run out, please put me down for as much warning as possible.

I have things to do...

thank you
Thank You...
  • Chuck Stewart MD EMDMProfessor of Emergency Medicine,University of Oklahoma
  • email [email protected]
  • [email protected]
  • Cell - 918-344-4557
  • Work - 918-660-3828
  • 2E24 Schusterman Center
  • 4502 E. 41st Street