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Chapter 10: Thunderstorms and Tornadoes Thunderstorms Thunderstorms Tornadoes Tornadoes Tornadic thunderstorms Tornadic thunderstorms Severe weather and.

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Presentation on theme: "Chapter 10: Thunderstorms and Tornadoes Thunderstorms Thunderstorms Tornadoes Tornadoes Tornadic thunderstorms Tornadic thunderstorms Severe weather and."— Presentation transcript:

1 Chapter 10: Thunderstorms and Tornadoes Thunderstorms Thunderstorms Tornadoes Tornadoes Tornadic thunderstorms Tornadic thunderstorms Severe weather and doppler radar Severe weather and doppler radar

2 Thunderstorms

3 Thunderstorms What do we already know about thunderstorms? What do we already know about thunderstorms? Can produce intense rain, hail, wind, lightning Can produce intense rain, hail, wind, lightning Can make tornadoes Can make tornadoes Formed by rising air from: Formed by rising air from: Uneven surface heating Uneven surface heating Uplift along a frontal boundary Uplift along a frontal boundary Topographical uplift Topographical uplift

4 Thunderstorms Definitions: Definitions: Supercell thunderstorms – large updraft storms that can produce flash floods, severe weather, tornadoes Supercell thunderstorms – large updraft storms that can produce flash floods, severe weather, tornadoes Severe Thunderstorm – has to have one of following: Severe Thunderstorm – has to have one of following: Hail greater than or equal to ¾ inch Hail greater than or equal to ¾ inch A tornado A tornado Wind gusts 50 mph Wind gusts 50 mph

5 Ordinary Cell Thunderstorms Ordinary cell thunderstorm Ordinary cell thunderstorm Form in region of low wind shear Form in region of low wind shear Can form due to surface air convergence Can form due to surface air convergence Cumulus stage (growth stage) – due to rising warm, humid air condensing into cumulus cloud Cumulus stage (growth stage) – due to rising warm, humid air condensing into cumulus cloud Latent heat release keeps cloud warm and unstable Latent heat release keeps cloud warm and unstable Grows quickly to towering cumulus Grows quickly to towering cumulus Usually no precipitation because of updrafts Usually no precipitation because of updrafts No lightning or thunder No lightning or thunder

6 Ordinary Cell Thunderstorms

7 Mature stage – marked by considerable downdrafts Mature stage – marked by considerable downdrafts Cloud particles grow larger, and begin to fall Cloud particles grow larger, and begin to fall Entrainment - Dry air is sucked into cloud, causing evaporation and cooling Entrainment - Dry air is sucked into cloud, causing evaporation and cooling Heavier and cooler air descends…downdrafts Heavier and cooler air descends…downdrafts Formation of updraft and downdraft cells Formation of updraft and downdraft cells Most intense time of thunderstorm Most intense time of thunderstorm Storm may grow as high as stratosphere (anvil) Storm may grow as high as stratosphere (anvil) Heavy rain, lightning, small hail Heavy rain, lightning, small hail

8 Ordinary Cell Thunderstorms Mature stage Mature stage Cloud top may overshoot into stratosphere Cloud top may overshoot into stratosphere

9 Ordinary Cell Thunderstorms Mature stage Mature stage Cloud top may overshoot into stratosphere Cloud top may overshoot into stratosphere Downdraft reaches ground and spreads along surface as a gust front Downdraft reaches ground and spreads along surface as a gust front Sometimes rain may not reach ground, but cold air does Sometimes rain may not reach ground, but cold air does

10 Ordinary Cell Thunderstorms

11 Dissipating stage – thunderstorm weakens Dissipating stage – thunderstorm weakens Updrafts begin to weaken after 15 to 30 min. Updrafts begin to weaken after 15 to 30 min. Gust front moves too far from the storm, so updrafts have to weaken Gust front moves too far from the storm, so updrafts have to weaken Light precipitation falls Light precipitation falls Only anvil remains Only anvil remains All three stages in less than an hour All three stages in less than an hour

12 Ordinary Cell Thunderstorms

13 Fig. 10-1, p. 265 Stepped Art

14 Severe Thunderstorms and the Supercell So ordinary cell storms weaken because the updraft weakens So ordinary cell storms weaken because the updraft weakens What if the updraft doesn’t weaken quickly? What if the updraft doesn’t weaken quickly? If moderate wind shear pushes downdraft downwind, updraft is not cut off If moderate wind shear pushes downdraft downwind, updraft is not cut off If downdraft then undercuts updraft, a multicell storm forms If downdraft then undercuts updraft, a multicell storm forms

15 Severe Thunderstorms and the Supercell

16 Multicell storms Multicell storms Cells of varying age co-mingling Cells of varying age co-mingling Top of cloud well into stratosphere Top of cloud well into stratosphere Updrafts allow hail to grow large Updrafts allow hail to grow large

17 Severe Thunderstorms and the Supercell Supercells Supercells If wind shear is strong and changes direction with height, downdraft may not undercut updraft If wind shear is strong and changes direction with height, downdraft may not undercut updraft Updraft remains strong for long time (> 1 hour) Updraft remains strong for long time (> 1 hour) One rotating vertical column One rotating vertical column Can create tornadoes Can create tornadoes Hail size of grapefruit Hail size of grapefruit

18 Severe Thunderstorms and the Supercell At surface, open wave with warm, humid air ahead of cold front At surface, open wave with warm, humid air ahead of cold front Overrunning warm air just above surface Overrunning warm air just above surface Dry air at 700 mb level Dry air at 700 mb level Trough of low pressure at 500 mb Trough of low pressure at 500 mb Divergence at 300 mb Divergence at 300 mb

19 Severe Thunderstorms and the Supercell Severe thunderstorms form in light green area because: Severe thunderstorms form in light green area because: Warm air below cold air is conditionally unstable Warm air below cold air is conditionally unstable Strong wind shear creates severe thunderstorms Strong wind shear creates severe thunderstorms In morning, atmos is stable, no thunderstorms In morning, atmos is stable, no thunderstorms Surface heating creates thunderstorms Surface heating creates thunderstorms

20 Squall Lines and Mesoscale Convective Complexes Squall line – line of multicell t-storms extending many kilometers Squall line – line of multicell t-storms extending many kilometers Mesoscale convective complex- cluster of storms in one spot Mesoscale convective complex- cluster of storms in one spot

21 Squall Lines and Mesoscale Convective Complexes Squall lines often form ahead of cold fronts (pre- frontal squall-line thunderstorms) Squall lines often form ahead of cold fronts (pre- frontal squall-line thunderstorms) MCCs are long-lasting and provide a lot of rain, and a ton of severe weather MCCs are long-lasting and provide a lot of rain, and a ton of severe weather Form during summer Form during summer

22 Dryline Thunderstorms Dryline – narrow zone with a sharp moisture contrast. Where do the thunderstorms form? Dryline – narrow zone with a sharp moisture contrast. Where do the thunderstorms form?

23 Gust Fronts, Microbursts and Derechoes Gust front – leading edge of the thunderstorm downdraft Gust front – leading edge of the thunderstorm downdraft Passage can feel like a cold front passage Passage can feel like a cold front passage Shelf cloud – warm air rising above gust front creates cloud Shelf cloud – warm air rising above gust front creates cloud Roll cloud – cloud just behind the gust front that spins horizontally Roll cloud – cloud just behind the gust front that spins horizontally Outflow boundary – a huge gust front formed by numerous thunderstorm gust front Outflow boundary – a huge gust front formed by numerous thunderstorm gust front Downbursts – localized downdraft like water from a tap Downbursts – localized downdraft like water from a tap Microbursts – downbursts that extend 4 km or less Microbursts – downbursts that extend 4 km or less

24 Gust Fronts, Microbursts and Derechoes

25

26 Fig , p. 271

27

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29 Microburst Microbursts can be dangerous to aircrafts Microbursts can be dangerous to aircrafts Plane encounters uplift at (a), and pilot puts nose down Plane encounters uplift at (a), and pilot puts nose down Unexpected downdraft crashes plane Unexpected downdraft crashes plane Has caused several airplane crashes Has caused several airplane crashes Some airports have microburst detection Some airports have microburst detection

30 Bow Echo and Derecho Bow echo – a line of thunderstorms often form a bow echo on radar Bow echo – a line of thunderstorms often form a bow echo on radar Derecho – winds associated with downdrafts that exceed 104 mph and can cause a lot of damage…20 derechoes each year in U.S. Derecho – winds associated with downdrafts that exceed 104 mph and can cause a lot of damage…20 derechoes each year in U.S.

31 Floods and Flash Floods Flash floods – floods that rise rapidly with little to no advance warning Flash floods – floods that rise rapidly with little to no advance warning Thunderstorms cause flash floods in two ways: Thunderstorms cause flash floods in two ways: Hovering above one area for a long time Hovering above one area for a long time Training – thunderstorms keep passing over same area Training – thunderstorms keep passing over same area

32 Distribution of Thunderstorms 18 millions thunderstorms worldwide annually 18 millions thunderstorms worldwide annually Need to have a combination of moisture and warmth Need to have a combination of moisture and warmth So do thunderstorms form in the Arctic? ITCZ? Gulf? So do thunderstorms form in the Arctic? ITCZ? Gulf?

33 Lightning and Thunder Lightning – simply a discharge of electricity, usually in mature thunderstorms Lightning – simply a discharge of electricity, usually in mature thunderstorms Heats air up to 54,000F (5x hotter that surface of sun Heats air up to 54,000F (5x hotter that surface of sun Thunder – the explosive expansion of the hot air creates a sound wave that travels in all direction Thunder – the explosive expansion of the hot air creates a sound wave that travels in all direction According to the Guinness Book of World Records, Roy Sullivan holds the world’s record for being struck by lightning seven times between 1942 and his death in 1983.According to the Guinness Book of World Records, Roy Sullivan holds the world’s record for being struck by lightning seven times between 1942 and his death in 1983.

34 Lightning and Thunder Light travels faster than sound, so we see the lightning before we hear the thunder Light travels faster than sound, so we see the lightning before we hear the thunder Sound takes 5 seconds to travel 1 mile Sound takes 5 seconds to travel 1 mile So if we hear thunder 5 seconds after we see the lightning, the stroke was 1 mile away So if we hear thunder 5 seconds after we see the lightning, the stroke was 1 mile away

35 Lightning and Thunder

36 Electrification of Clouds Must have charging of the cloud to have lightning Must have charging of the cloud to have lightning Electrification of clouds not fully understood Electrification of clouds not fully understood Theory 1: Supercooled droplets fall through cloud and collide with warm hailstone. Latent heat is released (warm or cold?) Theory 1: Supercooled droplets fall through cloud and collide with warm hailstone. Latent heat is released (warm or cold?)

37 Electrification of Clouds Net transfer of positive ions from warm to cold object Net transfer of positive ions from warm to cold object Falling hailstone is negatively charged, falls to bottom of cloud Falling hailstone is negatively charged, falls to bottom of cloud Light positively charge particle is lifted to top of cloud Light positively charge particle is lifted to top of cloud Small area of positively charge particles near melting level Small area of positively charge particles near melting level

38 Electrification of Clouds Theory 2: When precip forms, it has a neg in the upper portion and pos charge in the lower Theory 2: When precip forms, it has a neg in the upper portion and pos charge in the lower As droplets collide, the large droplets become neg and fall As droplets collide, the large droplets become neg and fall The small droplets are lifted by updrafts and rise The small droplets are lifted by updrafts and rise

39 The Lightning Stroke Basics of lightning Basics of lightning Opposite charges attract Opposite charges attract Positive charges on ground follow negative charges at base of cloud Positive charges on ground follow negative charges at base of cloud Electrical current will not flow because air is good insulator Electrical current will not flow because air is good insulator Charge must be large (< 1million volts per meter) to create a lightning bolt Charge must be large (< 1million volts per meter) to create a lightning bolt

40 The Lightning Stroke Cloud-to-ground lightning Cloud-to-ground lightning Discharge of electrons from cloud to ground as a stepped leader (many times) Discharge of electrons from cloud to ground as a stepped leader (many times) Positive charges race back up from elevated object as a return stroke Positive charges race back up from elevated object as a return stroke

41 The Lightning Stroke Cloud-to-ground lightning Cloud-to-ground lightning Many electrons flow to ground and a stronger return stoke follows (this is what you see) Many electrons flow to ground and a stronger return stoke follows (this is what you see) 1/10,000 of a second so it looks like one continuous flash 1/10,000 of a second so it looks like one continuous flash

42 The Lightning Stroke Dart leader – subsequent initial stroke that follows same path as initial stepped leader Dart leader – subsequent initial stroke that follows same path as initial stepped leader Causes the multiple flash of the lightning Causes the multiple flash of the lightning

43 Types of Lightning Forked lightning – dart leader takes different path than stepped leader Forked lightning – dart leader takes different path than stepped leader Ribbon lightning – wind blows charges into ribbon-like lightning Ribbon lightning – wind blows charges into ribbon-like lightning Dry lightning – lightning that occurs in a dry thunderstorm Dry lightning – lightning that occurs in a dry thunderstorm

44 Types of Lightning Heat lightning – lightning that is seen by not heard (can be orange) Heat lightning – lightning that is seen by not heard (can be orange) St. Elmo’s Fire – luminous green or blue halo around the top of pointed objects (antennas, masts of ships). Lightning may occur after this is seen. St. Elmo’s Fire – luminous green or blue halo around the top of pointed objects (antennas, masts of ships). Lightning may occur after this is seen.

45 Lightning Detection and Suppression Lightning direction-finder Lightning direction-finder

46 Tornado Life Cycles Tornado – rotating column of air blowing around a small low pressure that reaches the ground Tornado – rotating column of air blowing around a small low pressure that reaches the ground

47 Tornado Life Cycles Funnel cloud Funnel cloud Tornado that hasn’t reached the ground Tornado that hasn’t reached the ground Dust-whirl stage Dust-whirl stage Swirling dust at the ground marks the tornadoes circulation Swirling dust at the ground marks the tornadoes circulation Mature stage Mature stage Funnel at greatest width, most intense damage. Often vertical Funnel at greatest width, most intense damage. Often vertical Decay stage Decay stage Funnel shrinks, damage becomes less, tornado becomes stretched Funnel shrinks, damage becomes less, tornado becomes stretched

48 Tornado Outbreaks Tornado families – tornadoes spawned by the same thunderstorms Tornado families – tornadoes spawned by the same thunderstorms Tornado outbreaks – many tornadoes that form over same region Tornado outbreaks – many tornadoes that form over same region Much ground-breaking research on tornadoes was conducted by Professor Ted Fujita of the University of Chicago. The “F-scale” of tornado intensity was named after him.Much ground-breaking research on tornadoes was conducted by Professor Ted Fujita of the University of Chicago. The “F-scale” of tornado intensity was named after him.

49 Tornado Occurrence Tornado alley – part of the Central Plains from Texas through Nebraska Tornado alley – part of the Central Plains from Texas through Nebraska Time of day – most often in the afternoon Time of day – most often in the afternoon Times of year – most often in Spring, lease often in Winter Times of year – most often in Spring, lease often in Winter

50 Tornado Winds Multi-vortex tornadoes Multi-vortex tornadoes A single tornado with multiple rotating columns within it A single tornado with multiple rotating columns within it Suction vortices Suction vortices The small rotating columns within multi-vortex tornadoes The small rotating columns within multi-vortex tornadoes

51 Seeking Shelter Tornado watch – tornadoes are likely to develop within the next few hours Tornado watch – tornadoes are likely to develop within the next few hours Tornado warning – issued once a tornado is spotted Tornado warning – issued once a tornado is spotted It’s always a good idea to know what to do if a tornado watch or warning is issued for your area.It’s always a good idea to know what to do if a tornado watch or warning is issued for your area.

52 The Fujita Scale Tornado classification based on damage Tornado classification based on damage

53 Supercell Tornadoes Mesocyclones – Rising, rotating column on the south side of a supercell. Acts to increase the updraft Mesocyclones – Rising, rotating column on the south side of a supercell. Acts to increase the updraft Bounded weak echo region – area inside t-storm where radar does not pick up precip Bounded weak echo region – area inside t-storm where radar does not pick up precip Hook echo – Radar representation of a tornado (looks like a hook) Hook echo – Radar representation of a tornado (looks like a hook) Rotating clouds – First sign tornado is about to form Rotating clouds – First sign tornado is about to form Wall cloud – rotating clouds that have lowered below the base of a supercell Wall cloud – rotating clouds that have lowered below the base of a supercell A rotating wall cloud is an unforgettable sight - just ask a successful storm chaser.A rotating wall cloud is an unforgettable sight - just ask a successful storm chaser.

54 Fig , p. 290

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56 Nonsupercell Tornadoes Gustnadoes – tornadoes that flow along a gust front Gustnadoes – tornadoes that flow along a gust front Landspouts – similar to water spouts and form due to developing cumulus congestus Landspouts – similar to water spouts and form due to developing cumulus congestus

57 Severe Weather and Doppler Radar Doppler shift – Change in frequency in sound waves for moving objects Doppler shift – Change in frequency in sound waves for moving objects Tornado vortex signature – rapidly changing wind direction in mesocyclone Tornado vortex signature – rapidly changing wind direction in mesocyclone NEXRAD – Network of 150 radar stations in U.S. NEXRAD – Network of 150 radar stations in U.S. Waterspout – Tornado that forms over water Waterspout – Tornado that forms over water


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