Tornadoes The recent Oklahoma experience With a Tribute

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 • 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 Three stages have been identified in ordinary thunderstorms: 1. an unstable atmosphere and vertical updrafts keep precipitation suspended 2. entrainment of dry air that causes cooler air from evaporation, triggering downdrafts and falling precipitation and gust fronts 3. weakening updrafts and loss of the fuel source after 15 to 30 minutes.

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 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 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 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 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 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 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 • 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 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 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.

Tornado 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” Recent research shows that there are really 4 separate tornado alleys… Tornado alley Hoosier alley Dixie alley Carolina alley

Transition. . . How we get from. . • To here:

Wind Shear initiates rotation. . . Remember wind shear formation --- the ‘roll cloud’ -

Rising air elevates 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 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

And. . . A tornado is spawned

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. . . 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 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 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 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 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 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.

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.

Fast Scan of Radar 3 May 99

Moore 1999 (from space)

1 May 2010

Waterspout 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.

Just how bad is this tornado? ? ?

Fujita Tornado Scale

Comparing Beaufort, Fujita, and Mach Scales These scales have wind speed defined first, impacts/damage were assigned to wind speeds. M 1. 0 Beaufort: V = 1. 870 B 3/2 F – scale: V = 14. 1(F+2)3/2 Mach scale: V = (742 +1. 3)M F 12 M 0. 8 mph mph M 0. 7 M 0. 6 F 5 F 4 B 5 B 3 B 1 B 9 B 7 0 0 1 2 3 4 5 6 7 8 Beaufort Scale 9 F 3 B 11 F 0 B 17 F 2 F 1 1 10 11 12 2 3 4 5 6 7 8 Fujita Scale 9 10 11 12 0. 6 1. 0 Mach Scale

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 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 Residences Commercial/retail structures Schools Professional buildings Metal buildings/canopies Towers/poles Vegetation

Each indicator has “Degrees Of Damage” Note some consecutive DODs have larger overlap than others DOD Damage Description EXP LB UB 1 Threshold of visible damage 63 53 80 2 Loss of roof covering material (<20%), gutters and/or awning; loss of vinyl or metal siding 79 63 97 3 Broken glass in doors and windows 96 79 114 4 Uplift of roof deck and loss of significant roof covering material (>20%); collapse of chimney; garage doors collapse inward or outward; failure of porch or carport 97 81 116 5 Entire house shifts off foundation 121 103 141 6 Large sections of roof structure removed; most walls remain standing 122 104 142 7 exterior walls collapsed 132 113 153 8 Most walls collapsed except small interior rooms. 152 127 178 9 All walls collapsed 170 142 198 10 Destruction of engineered and/or well constructed residence; slab swept clean 200 162 220 Example DODs for a Framed House DI (FR 12 or DI 2)

“Degrees Of Damage” DOD Damage Description – Framed House EXP LB UB 1 Threshold of visible damage 63 53 80 2 Loss of roof covering material (<20%), gutters and/or awning; loss of vinyl or metal siding 79 63 97 3 Broken glass in doors and windows 96 79 114 4 Uplift of roof deck and loss of significant roof covering material (>20%); collapse of chimney; garage doors collapse inward or outward; failure of porch or carport 97 81 116 5 Entire house shifts off foundation 121 103 141 6 Large sections of roof structure removed; most walls remain standing 122 104 142 7 exterior walls collapsed 132 113 153 8 Most walls collapsed except small interior rooms. 152 127 178 9 All walls collapsed 170 142 198 10 Destruction of engineered and/or well constructed residence; slab swept clean 200 162 220 Expected wind 97 mph

F to EF Conversion F Scale Wind Speed F 0 F 1 F 2 F 3 F 4 F 5 45 -78 79 -117 118 -161 162 -209 210 -261 262 -317 EF-Scale Wind Speed EF 0 EF 1 EF 2 EF 3 EF 4 EF 5 Wind speeds in mph, 3 -second gust 65 -85 86 -109 110 -137 138 -167 168 -199 200 -234

Picher, OK 10 May 2008 • BEFORE…

Picher, OK 10 May 2008

Picher, OK Vital Statistics Population (year 2000): 1, 640. Estimated population in July 2006: 1, 633 (-0. 4% change) Males: 800 Females: 840 (48. 8%) (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 Tornado

Lone Grove Tornado EF 4 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.

OKC-Edmond

Lone Grove ‘hook’

? ? Lone Grove Tornado ? ?

Lone Grove Tornado Path

Lone Grove

Power line hazards

Trailer Damage

“Degrees Of Damage” DOD Damage Description – Framed House EXP LB UB 1 Threshold of visible damage 63 53 80 2 Loss of roof covering material (<20%), gutters and/or awning; loss of vinyl or metal siding 79 63 97 3 Broken glass in doors and windows 96 79 114 4 Uplift of roof deck and loss of significant roof covering material (>20%); collapse of chimney; garage doors collapse inward or outward; failure of porch or carport 97 81 116 5 Entire house shifts off foundation 121 103 141 6 Large sections of roof structure removed; most walls remain standing 122 104 142 7 exterior walls collapsed 132 113 153 8 Most walls collapsed except small interior rooms. 152 127 178 9 All walls collapsed 170 142 198 10 Destruction of engineered and/or well constructed residence; slab swept clean 200 162 220 All walls collapsed Expected wind 170 mph

Frame House

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

Monthly Tornado Deaths 2009 2008 2007 2006 3 Year preliminary Actual Average Jan 10 84 21 47 51 Feb 44 147 52 12 70 Mar 33 so far 129 170 150 149 Apr 189 167 245 200 May 461 252 139 284 Jun 294 128 120 181 Jul 93 69 71 77 Aug 101 75 80 85 Sep 111 52 84 82 Oct 21 86 76 61 Nov 15 7 42 21 Dec 46 19 40 36 Tot 1691 1098 1106 1297

1 May 2010 Ark – 1 dead

1 May 2010 Ark

1 May 2010 Ark

1 May 2010 Ark

1 May 2010 Ark

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 "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 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. WE NEED TO FIX THIS!

It may be a busy season…

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. . . Chuck Stewart MD EMDM Professor of Emergency Medicine, University of Oklahoma email charles-e-stewart@ouhsc. edu cstew@storysmith. net Cell - 918 -344 -4557 Work - 918 -660 -3828 2 E 24 Schusterman Center 4502 E. 41 st Street

Moore 1999