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Published byKathleen Porter Modified over 9 years ago
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Average annual # of days with thunderstorms
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Deaths from Natural Hazards in the US
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Air mass thunderstorms: (90% of all t-storms are of this type) —occur as mT air masses are heated from below by warm land surfaces --usually are of short duration and do not produce hail, damaging winds, or tornadoes --isolated distribution
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Severe thunderstorms (10% of all t-storms are of this type) —may involve convection due to surface heating, but uplift is enhanced by frontal activity or orography --typically produce winds + 58 mph, and hail --storms may be aligned along a front
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Life Cycle of a Thunderstorm 1. Cumulus stage—water vapor is moved aloft by updrafts; vertical cumulus development
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2.Mature stage—once the cloud reaches the freezing level precipitation forms via the Bergeron process; falling precipitation produces a drag on the surrounding air causing cold downdrafts; Entrainment—cold air from outside the storm aloft is pulled into the storm and moves down as part of the downdraft
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3. Dissipating stage—downdrafts dominate and moisture input from surface ceases
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“Anvil head”
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Help me!
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A roll cloud may signal the advance of a gust front
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In some areas, the break up of a temperature inversion in the afternoon can lead to thunderstorm development
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One thunderstorm can spawn other ‘daughter’ cells through the formation of a gust front
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In summer, cT air masses from the arid SW US can be drawn into low-pressure systems in the Great Plains states. This creates a dryline boundary (between cT air and less dense mT air) where violent thunderstorms may develop.
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if a dryline exists, storm development along the cold front will be minimal squall line: line of intense thunderstorms
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Mesoscale Convective Complex— --a very large (~40,000 mi 2 ) organized cluster of severe thunderstorms
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MCC over Oklahoma
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MCC
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Imbedded in a squall line or an MCC, large, rotating thunderstorms called mesocylcones may form (1/2 of all mesocyclones produce tornadoes)
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Mesocyclone: (typically 10-30 miles wide and 70,000 feet tall!)
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Thunderstorm hazards
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Hail forms as ice crystals are swept aloft numerous time by updrafts
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Concentric rings of a hailstone
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Mircroburst—a narrow, high speed downdraft (may exceed 100 mph)
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Downbursts can create straight-line winds called derechos (may be +100mph) derechos are often mistaken for tornadoes
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Destruction path of a derecho
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Derecho damage
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Lightning –electrical stroke between oppositely charged particles charge separation is caused by updrafts, downdrafts
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Lightning heats the air to 50,000º F
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if you feel static electricity like this person get to a low area immediately
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Lightning Safety
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Thunder—sound of air expanding upon heating by lightning strike (sound waves travel about 1000 ft/sec)
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