Chapter 14
Wall Cloud associated with a super cell thunderstorm
Thunderstorms
A storm containing lightening and thunder; convective storms may have heavy rain hail
Ordinary Cell ThunderstormsAir-mass thunderstorms: limited wind sheerStages: cumulus, mature, dissipatingEntrainment, downdraft, gust front
A dissipating thunderstorm
Thunderstorms
Multi-cell ThunderstormsThunderstorms that contain a number of
convection cells, each in a different stage of development, moderate to strong wind shear; tilt, over shooting top
Multicell storm
Thunderstorms
Multi-cell ThunderstormsMicro-bursts: localized downdraft that hits
the ground and spreads horizontally in a radial burst of wind; wind shear, virga
Dust clouds from microbursts
Thunderstorms
Multi-cell ThunderstormsGust Front: leading edge of the cold air out-
flowing air; shelf cloud, roll cloud, outflow boundary
Thunderstorms
Severe thunderstorms: one of large hail, wind gusts greater than or equal to 50kts, or tornado, tilted updraft/downdraft
Shelf cloud
Thunderstorms
Multi-cell ThunderstormsSquall-line thunderstorms; line of multi-cell
thunderstorms, pre-frontal squall-line, derecho
Pre frontalSquall line
Pre frontalSquall line
The thunderstorms are producing strong straight-line winds called a derecho
Thunderstorms
Multi-cell ThunderstormsMeso-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
Thunderstorms
Supercell thunderstormsLarge, long-lasting thunderstorm with a
single rotating updraftStrong vertical wind shearOutflow never undercuts updraftClassic, high precipitation and low
precipitation supercellsRain free base
A supercell thunderstormwith a tornado sweeps over Texas
Thunderstorms
Supercell thunderstormsStrong vertical wind shearSurface, 850mb, 700mb, 500mb, 300mb
conditions low-level jet
Thunderstorms
Supercell thunderstormsCap and convective instability
Thunderstorms
Thunderstorms and the DrylineSharp, horizontal change in moistureThunderstorms form just east of drylinecP, mT, cT
Fig. 14-23, p. 384
Thunderstorms
Floods and Flash FloodsLarge floods can be created by training of
storm systems, Great Flood of 1993
Flash floods rise rapidly with little or no advance warning; many times caused by stalled or slow thunderstorm
Fig. 14-25, p. 387
downtown Des Moines, Iowa, during July, 1993
Thunderstorms
Topic: Big Thompson CanyonJuly 31, 1976, 12 inches of rain in 4 hours
created a flood associated with $35.5million in damage and 135 deaths
Fig. 1, p. 386
Flash FloodsSlow moving or Stalled thunder Storm, especially in canyon areas
135 deaths in 1976 flood12 inches of rain in 4 hours(normal ~16 inches /year)
Thunderstorms
Distribution of ThunderstormsMost frequent Florida, Gulf Coast, Central
PlainsFewest Pacific coast and Interior valleysMost frequent hail Central Plains
Thunderstorms
Lightening and ThunderLightening: discharge of electricity in mature
storms (within cloud, cloud to cloud, cloud to ground)
Thunder: explosive expansion of air due to heat from lightening
Electrification of Clouds: graupel and hailstones fall through supercooled water, ice crystals become negatively charged
Upper cloud positive, bottom cloud negative
Thunderstorms
Observations: ElvesBlue jets, red sprite, ELVES
Fig. 2, p. 390
Thunderstorms
The Lightening StrokePositive charge typically on ground, cloud to
ground lighteningStepped leader, ground stroke, forked
lightening, ribbon lightening, bead lightening, corona discharge
Thunderstorms
Observation: Apple treeDO 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
Fig. 3, p. 395
Fig. 14-32, p. 392
Fig. 14-33, p. 393
Fig. 14-34, p. 393
fulgurite
Fig. 14-35, p. 394
Fig. 14-36, p. 394
sferics