Presentation on theme: "Thunderstorms and Tornadoes"— Presentation transcript:
1Thunderstorms and Tornadoes Chapter 14Thunderstorms and Tornadoes
2Wall Cloud associated with a super cell thunderstorm
3ThunderstormsA storm containing lightening and thunder; convective storms may have heavy rain hailOrdinary Cell ThunderstormsAir-mass thunderstorms: limited wind sheerStages: cumulus, mature, dissipatingEntrainment, downdraft, gust front
4FIGURE 14.2 Simplified model depicting the life cycle of an ordinary cell thunderstorm that is nearly stationary as it forms in a regionof low wind shear. (Arrows show vertical air currents. Dashed line represents freezing level, 0oC isotherm.)
5A dissipating thunderstorm FIGURE 14.3 A dissipating thunderstormnear Naples, Florida. Most of the cloudparticles in the lower half of the storm haveevaporated.A dissipating thunderstorm
6Thunderstorms Multi-cell Thunderstorms Thunderstorms that contain a number of convection cells, each in a different stage of development, moderate to strong wind shear; tilt, over shooting top
10Thunderstorms Multi-cell Thunderstorms Gust Front: leading edge of the cold air out-flowing air; shelf cloud, roll cloud, outflow boundary
11ACTIVE FIGURE 14.5 A simplified model describing air motions and other features associated with an intense multicellthunderstorm that has a tilted updraft. The severity depends on the intensity of the storm’s circulation pattern. Visit the MeteorologyResource Center to view this and other active figures at academic.cengage.com/login
12ThunderstormsSevere thunderstorms: one of large hail, wind gusts greater than or equal to 50kts, or tornado, tilted updraft/downdraft
13Shelf cloud FIGURE 14.7 A dramatic example of a shelf cloud (or arcus cloud) associatedwith an intense thunderstorm. Thephotograph was taken in the Philippinesas the thunderstorm approached from thenorthwest.Shelf cloud
14FIGURE 14.8 A roll cloud forming behind a gust front.
15FIGURE 14.9 Radar image of an outflow boundary. As cool (more-dense) air from inside the severe thunderstorms (red and orangecolors) spreads outward, away from the storms, it comes in contact withthe surrounding warm, humid (less-dense) air, forming a densityboundary (blue line) called an outflow boundary between cool air andwarm air. Along the outflow boundary, new thunderstorms often form.
16Thunderstorms Multi-cell Thunderstorms Squall-line thunderstorms; line of multi-cell thunderstorms, pre-frontal squall-line, derecho
17Pre frontal Squall line FIGURE A Doppler radar composite showing a prefrontalsquall line extending from Indiana southwestward into Arkansas.Severe thunderstorms (red and orange colors) associated with the squallline produced large hail and high winds during October, 2001.Pre frontalSquallline
18FIGURE 14.13 Pre-frontal squall-line thunderstorms may form ahead of an advancing cold front as the upper-air flow develops wavesdownwind from the cold front.
20FIGURE 14.14 A model describing air motions and precipitation associatedwith a squall line that has a trailingstratiform cloud layer.
21FIGURE 14.15 A side view of the lower half of a squall-line thunderstorm with therear-inflow jet carrying strong winds fromhigh altitudes down to the surface. Thesestrong winds push forward along the surface,causing damaging straight-line winds that mayreach 100 knots. If the high winds extendhorizontally for a considerable distance, thewind storm is called a derecho.
22FIGURE 14.16 The red and orange on this Doppler radar image show an intense squall line moving south southeastward into Kentucky.The thunderstorms are producing strong straight-line winds called aderecho. Notice that the line of storms is in the shape of a bow. Suchbow echos are an indicator of strong, damaging surface winds near thecenter of the bow. Sometimes the left (usually northern) side of thebow will develop cyclonic rotation and produce a tornado.The thunderstorms are producing strong straight-line winds called a derecho
23Thunderstorms Multi-cell Thunderstorms Meso-scale Convective Complex: a number of individual multi-cell thunderstorms grow in size and organize into a large circular convective weather system; summer, 10,000km2
24FIGURE 14.17 An enhanced infrared satellite image showing the cold cloud tops (dark red and orange colors) of a MesoscaleConvective Complex extending from central Kansas across westernMissouri. This organized mass of multicell thunderstorms broughthail, heavy rain, and flooding to this area.
25Thunderstorms Supercell thunderstorms Large, long-lasting thunderstorm with a single rotating updraftStrong vertical wind shearOutflow never undercuts updraftClassic, high precipitation and low precipitation supercellsRain free base
26A supercell thunderstormwith a tornado sweeps over Texas FIGURE A supercell thunderstormwith a tornado sweeps over Texas.
27FIGURE Some of the features associated with a classic tornado-breeding supercell thunderstorm as viewed from the southeast.The storm is moving to the northeast.
28FIGURE 14.20 A wall cloud photographed southwest of Norman, Oklahoma.
30FIGURE 14.21 Conditions leading to the formation of severe thunderstorms, and especially supercells. The area in yellow showswhere supercell thunderstorms are likely to form.
31ThunderstormsSupercell thunderstormsCap and convective instability
32FIGURE 14.22 A typical sounding of air temperature and dew point that frequently precedes the development of supercellthunderstorms.
33Thunderstorms Thunderstorms and the Dryline Sharp, horizontal change in moistureThunderstorms form just east of drylinecP, mT, cT
34Figure 14.23Surface conditions that can produce a dryline with intense thunderstorms.Fig , p. 384
35Thunderstorms Floods and Flash Floods Large floods can be created by training of storm systems, Great Flood of 1993Flash floods rise rapidly with little or no advance warning; many times caused by stalled or slow thunderstorm
36FIGURE 14.24 The heavy arrow represents the average position of the upper-level jet stream from mid-June through July, The jetstream helped fuel thunderstorms that developed in association with astationary front that seemed to oscillate back and forth over the regionas an alternating cold front and warm front. The 鏑� marks the center ofa frontal wave that is moving along the front. Many of the thunderstormsthat formed in conjunction with this pattern were severe, andover a period of weeks produced 典he Great Flood of 1993.� Most ofthe counties within the blue-shaded area were declared 電isaster areas�due to flooding.
37downtown Des Moines, Iowa, during July, 1993 Figure 14.25Flooding during the summer of 1993 covered a vast area of the upper Midwest. Here, floodwaters near downtown Des Moines, Iowa, during July, 1993, inundate buildings of the Des Moines waterworks facility. Flood-contaminated water left 250,000 people without drinking water.downtown Des Moines, Iowa, during July, 1993Fig , p. 387
38Thunderstorms Topic: Big Thompson Canyon July 31, 1976, 12 inches of rain in 4 hours created a flood associated with $35.5million in damage and 135 deaths
39Figure 1Weather conditions that led to the development of intense thunderstorms that remained nearly stationary over the Big Thompson Canyon in the Colorado Rockies. The arrows within the thunderstorm represent air motions.Fig. 1, p. 386
40Flash FloodsSlow moving or Stalled thunder Storm, especially in canyon areas135 deaths in 1976 flood12 inches of rain in 4 hours(normal ~16 inches /year)
44Thunderstorms Distribution of Thunderstorms Most frequent Florida, Gulf Coast, Central PlainsFewest Pacific coast and Interior valleysMost frequent hail Central Plains
45FIGURE 14.26 The average number of days each year on which thunderstorms are observedthroughout the United States. (Due to thescarcity of data, the number of thunderstorms isunderestimated in the mountainous far west.)
46FIGURE 14.27 The average number of days each year on which hail is observedthroughout the United States.
52Thunderstorms Lightening and Thunder Lightening: discharge of electricity in mature storms (within cloud, cloud to cloud, cloud to ground)Thunder: explosive expansion of air due to heat from lighteningElectrification of Clouds: graupel and hailstones fall through supercooled water, ice crystals become negatively chargedUpper cloud positive, bottom cloud negative
54FIGURE 14.28 The lightning stroke can travel in a number of directions. It can occur within a cloud, from one cloud to anothercloud, from a cloud to the air, or from a cloud to the ground. Noticethat the cloud-to-ground lightning can travel out away from the cloud,then turn downward, striking the ground many miles from the thunderstorm.When lightning behaves in this manner, it is often describedas a “bolt from the blue.”
55FIGURE 14.29 When the tiny colder ice crystals come in contact with the much larger and warmer hailstone (or graupel), the icecrystal becomes positively charged and the hailstone negatively charged.Updrafts carry the tiny positively charged ice crystal into the upperreaches of the cloud, while the heavier hailstone falls through theupdraft toward the lower region of the cloud.
56FIGURE 14.30 The generalized charge distribution in a mature thunderstorm.
57ThunderstormsObservations: ElvesBlue jets, red sprite, ELVES
58Figure 2Various electrical phenomena observed in the upper atmosphere.Fig. 2, p. 390
59Thunderstorms The Lightening Stroke Positive charge typically on ground, cloud to ground lighteningStepped leader, ground stroke, forked lightening, ribbon lightening, bead lightening, corona discharge
60ACTIVE FIGURE 14. 31 The development of a lightning stroke ACTIVE FIGURE The development of a lightning stroke. (a) When the negative charge near the bottom of thecloud becomes large enough to overcome the air’s resistance, a flow of electrons — the stepped leader — rushes toward the earth.(b) As the electrons approach the ground, a region of positive charge moves up into the air through any conducting object, suchas trees, buildings, and even humans. (c) When the downward flow of electrons meets the upward surge of positive charge, astrong electric current — a bright return stroke — carries positive charge upward into the cloud. Visit the Meteorology ResourceCenter to view this and other active figures at academic.cengage.com/login
61Thunderstorms Observation: Apple tree DO NOT seek shelter during a thunderstorm under an isolated tree.Lightening Detection and SuppressionLightening direction finder detects radiowaves produced by lightening, sphericsNational Lightening Detection NetworkSuppression: seed clouds with aluminum
62ACTIVE FIGURE 14. 31 The development of a lightning stroke ACTIVE FIGURE The development of a lightning stroke. (a) When the negative charge near the bottom of thecloud becomes large enough to overcome the air’s resistance, a flow of electrons — the stepped leader — rushes toward the earth.(b) As the electrons approach the ground, a region of positive charge moves up into the air through any conducting object, suchas trees, buildings, and even humans. (c) When the downward flow of electrons meets the upward surge of positive charge, astrong electric current — a bright return stroke — carries positive charge upward into the cloud. Visit the Meteorology ResourceCenter to view this and other active figures at academic.cengage.com/login
63Figure 3A cloud-to-ground lightning flash hitting a 65-foot sycamore tree. It should be apparent why one should not seek shelter under a tree during a thunderstorm.Fig. 3, p. 395
64Figure 14.32Time exposure of an evening thunderstorm with an intense lightning display near Denver, Colorado. The bright flashes are return strokes. The lighter forked flashes are probably stepped leaders that did not make it to the ground.Fig , p. 392
65Figure 14.33The lightning rod extends above the building, increasing the likelihood that lightning will strike the rod rather than some other part of the structure. After lightning strikes the metal rod, it follows an insulated conducting wire harmlessly into the ground.Fig , p. 393
67Figure 14.34A fulgurite that formed by lightning fusing sand particles.fulguriteFig , p. 393
68Figure 14.35The four marks on the road surface represent areas where lightning, after striking a car traveling along south Florida’s Sunshine State Parkway, entered the roadway through the tires. Lightning flattened three of the car’s tires and slightly damaged the radio antenna. The driver and a six-year-old passenger were taken to a nearby hospital, treated for shock, and released.Fig , p. 394
69Figure 14.36Cloud-to-ground lightning strikes in the vicinity of Chicago, Illinois, as detected by the National Lightning Detection Network.sfericsFig , p. 394
70FIGURE 14.26 The average number of days each year on which thunderstorms are observedthroughout the United States. (Due to thescarcity of data, the number of thunderstorms isunderestimated in the mountainous far west.)