Transcript Slide 1

NOAA
What are we
looking at?
inewscatcher.com
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Tornadoes
18/07/2015
Learning Objectives:
•What conditions lead to
tornadoes?
•In what way do they represent
a hazard to people?
Tornado Definition:
A rotating column of air
ranging in width from a
few yards to more than a
mile and whirling at
destructively high speeds,
usually accompanied by a
funnel-shaped downward
extension of a
cumulonimbus cloud
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Tornadoes can occur on nearly any landmass on
Earth (except in polar regions).
Tornadoes in the UK - This animation shows the
location of all confirmed UK tornadoes. Click on
the 2nd UK map down the page.
http://www.torro.org.uk/site/index.php
TORRO – the UK TORnado and storm
Research Organisation
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Regions of the world with increased likelihood of
experiencing tornadoes.
Source - NOAA
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Tornado
Alley
Source: FEMA
Figure 2 – Tornado tracks from 1950- 2004 Courtesy of
NOAA
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US tornadoes by month
Source:
NOAA 8
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Average number of tornadoes 20032005
20
22
54
109
180
171
96
60
41
29
30
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No. of tornadoes in St Louis warning area by hour
Time of day
00:00:00
01:00:00
02:00:00
03:00:00
04:00:00
05:00:00
06:00:00
07:00:00
08:00:00
09:00:00
10:00:00
11:00:00
No. of tornadoes in St
Louis warning area
7
4
9
0
1
1
1
1
0
1
3
10
Source: NOAA
Time of day
12:00:00
13:00:00
14:00:00
15:00:00
16:00:00
17:00:00
18:00:00
19:00:00
20:00:00
21:00:00
22:00:00
23:00:00
No. of tornadoes in St
Louis warning area
2
6
7
13
15
23
18
16
9
9
10
2
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hunderstorm Formation NOAA
NWS
Animation - Click here
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For a thunderstorm to form, warm moist air is required.
When cooler air arrives higher in the atmosphere,
instability develops and therefore convection (warmer air
rising) takes place forming a cumulonimbus cloud i.e. a
thunderstorm.
Synoptic conditions required for supercell
(and therefore tornado) formation
NSSL
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Link to an explanation by a US meteorologist of how a
tornado can form
NSSL
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A surface low
pressure system
develops to the
East of the Rocky
Mountains
NSSL
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This causes warm, moist air to be dragged up from
the Gulf of Mexico, warm/hot dry air from the
desert states and cold, dry air down from the
Rocky Mountains.
These three air
masses converge
over the Southern
States (e.g.
Oklahoma and
Texas) and cause
instability in the
atmosphere to
develop.
NSSL
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NOAA
NWS
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Convection occurs during the peak heating time
of the day (mid-afternoon). This results in
cumulonimbus clouds developing.
If the wind varies in direction and strength with increasing
height (this is called wind shear), then the updraft (rising
air) and downdraft (sinking air containing rain and hail) will
separate. The updraft may also rotate. We now have a
supercell thunderstorm.
NSSL
Animation
of this
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This rotating updraft is called a mesocyclone and can be
seen using Doppler Radar. If these are seen then a Tornado
Warning is issued for the county under the supercell
thunderstorm.
NSSL
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Rainfall radar
showing rainfall
intensity
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Doppler Radar
showing wind
direction. Where
red and green
touch, winds are
moving rapidly in
opposite
directions
indicating a
mesocyclone and
possible tornado.
If warm moist air
continues to flow into
the mesocyclone
(rotating updraft) then
it can become
stretched, becoming
thinner and rotating
more quickly (just like
water down a bath plug
hole).
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The stretched
mesocyclone can begin
to descend to the
ground. The air
pressure inside it starts
to fall rapidly and so
water vapour cools,
condenses and
therefore becomes
visible. A funnel cloud
has formed.
NSSL
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NOAA
If this continues to
descend to touch the
ground then we have a
tornado. Wind speeds
can vary from a few
mph to over 300mph.
Wind speeds are
estimated from
damage surveys and
referring the
Enhanced Fujita Scale
(EF Scale)
inewscatcher.com
Hail to 4inches diameter!
And frequent lightning
are also a threat from
supercells
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Diagram of a classic supercell
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Updraft
Downdraft
The Enhanced Fujita Scale – Storm Prediction Center (SPC)
Student
activity to
rate tornado
based on
damage
photos –
Click here
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Oklahoma City May 3rd 1999 EF5 Tornado – Click Here
Oklahoma/Kansas Tornado Outbreak
May 3rd 1999
•74 tornadoes in less than 21 hours
•Four of the tornadoes were on the
ground at the same time!
•There was an EF5 tornado which was
on the ground for 1 ½ hours and tracked
38 miles.
Oklahoma/Kansas Tornado Outbreak
May 3rd 1999
•46 people died
•800 people injured
•8000 buildings damaged or destroyed
•$1.5 billion of
NSSL
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damage
Damage near Oklahoma
City on 3rd May 1999
Supercells
NOAA
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Oklahoma
Storms so
severe that
updrafts are
breaking
through into
the
stratosphere
Dryline – Border between moist and dry air and
thunderstorms usually form just ahead of this.
Social
-Deaths/injuries and associated pressure on
public services
-Closure of road and rail networks
-Widespread power cuts
-Homelessness and closure of businesses
Economic
-Damage to infrastructure
-Damage and loss to businesses and crops
-Positive for building industry
Environmental
-Widespread loss of woodland
-Possible contamination if any chemical storage
(e.g. Farm pesticides/fertilisers) have been
damaged.
Tornado prediction and the US
Watch/Warning system
Up to three days in advance the Storm Prediction Centre
in Norman, Oklahoma issues a Convective Outlook as
below.
The highest risk
for severe weather
(tornadoes, hail >1
inch diameter and
damaging wind
gusts) is clearly
labelled.
NOAA – 20
Tornado prediction and the US
Watch/Warning system
If conditions remain
favourable for tornadoes
then a few hours before
thunderstorms develop a
Tornado Watch is issued
detailing the threats. Local
authorities can now start to
put action plans into place,
making public aware of the
risk and this is also
broadcast on local radio and
TV.
NOAA - 21
Tornado prediction and the US
Watch/Warning system
If a supercell thunderstorm
forms and a mesocyclone is
detected by weather radar
then a tornado warning is
issued. This means a tornado
is imminent or already on the
ground. Tornado sirens are
then usually set off to inform
everybody that they should
seek shelter in a basement
immediately.
Tornado warned county
NOAA - 22
NOAA
Homework – Due
Research either:
•The Birmingham, UK tornado 28-07-2005
•The Greensburg, Kansas May 4th 2007 EF5 Tornado
•Extension – Research in detail why the USA gets more
tornadoes and why they are generally more violent than
anywhere else on Earth. OR discuss the pro’s and con’s in
living in a region which experiences extreme weather –
should we continue building there?
Tornado Siren – Click here
Extreme Hailstorm– Click here
Tornado Chasers – Click here
Sources:
1)NSSL - http://www.nssl.noaa.gov/headlines/images/dsz8.jpg
2)SPC - http://www.spc.noaa.gov/faq/tornado/seymour.jpg
3)David Hoadley http://www.spc.noaa.gov/faq/tornado/waurikae.jpg
4)NSSL - http://www.spc.noaa.gov/faq/tornado/waurikaw.jpg
5)NOAA http://www.ncdc.noaa.gov/img/climate/research/tornado/globdis
t.jpg
6)FEMA http://www.fema.gov/plan/prevent/saferoom/tsfs02_torn_activity.
shtm
7)NOAA – http://www.spc.noaa.gov/gis/svrgis/
8)NOAA –
http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.h
tml
Sources:
9) NOAA –
http://www.ncdc.noaa.gov/oa/climate/severeweather/tornado
es.html
10) NWS - http://www.srh.weather.gov/jetstream/tstorms/life.htm
11) NSSL http://www.nssl.noaa.gov/primer/tornado/images/tor_alley_lg
.gif
12) NSSL http://www.nssl.noaa.gov/primer/tornado/images/tor_formati
on_lg.jpg
13) SPC - http://www.spc.noaa.gov/faq/tornado/doppler.htm
14) Microsoft PowerPoint ClipArt
15) http://www.spc.noaa.gov/faq/tornado/kngsmill.jpg
Sources:
16) NSSL - http://www.spc.noaa.gov/faq/tornado/suprcell.htm
17) SPC - http://www.spc.noaa.gov/faq/tornado/f-scale.html
18) NSSL - http://www.nssl.noaa.gov/news/may3rd/damage3.jpg
19) NOAA - http://www.nssl.noaa.gov/news/may3rd/satellite.html
20) SPC http://www.spc.noaa.gov/products/outlook/archive/2010/day1
otlk_20100519_1630.html
21) SPC - http://www.spc.noaa.gov/products/watch/ww0190.html
22) SPC - http://www.spc.noaa.gov/products/watch/ww0190.html