Transcript Tornado May2010

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 3May99
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.
M1.0
F12
Beaufort:
V = 1.870B3/2
F – scale: V = 14.1(F+2)3/2
Mach scale: V = (742 +1.3)M
M0.8
mph
mph
mph
M0.7
M0.6
F5
B17
F4
B5
B3
B1
B9
B7
F3
B11
F0
0
F2
F1
1
2
3
4
5
6
7
8
9
10 11 12
Fujita Scale
0
1
2
3
4
5
6 7
8
Beaufort 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 (FR12 or DI2)
“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
F0
F1
F2
F3
F4
F5
45-78
79-117
118-161
162-209
210-261
262-317
EF-Scale Wind Speed
EF0
EF1
EF2
EF3
EF4
EF5
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
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.
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
3Year
preliminary
Actual
Actual
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
1May2010 Ark – 1 dead
1May2010 Ark
1May2010 Ark
1May2010 Ark
1May2010 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 [email protected]
[email protected]
Cell - 918-344-4557
Work - 918-660-3828
2E24 Schusterman Center
4502 E. 41st Street
Moore 1999