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Slide 2 Average annual # of days with thunderstorms Slide 3 Deaths from Natural Hazards in the US Slide 4 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 Slide 5 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 Slide 6 Life Cycle of a Thunderstorm 1. Cumulus stagewater vapor is moved aloft by updrafts; vertical cumulus development Slide 7 2.Mature stageonce the cloud reaches the freezing level precipitation forms via the Bergeron process; falling precipitation produces a drag on the surrounding air causing cold downdrafts; Entrainmentcold air from outside the storm aloft is pulled into the storm and moves down as part of the downdraft Slide 8 3. Dissipating stagedowndrafts dominate and moisture input from surface ceases Slide 9 Slide 10 Anvil head Slide 11 Help me! Slide 12 A roll cloud may signal the advance of a gust front Slide 13 In some areas, the break up of a temperature inversion in the afternoon can lead to thunderstorm development Slide 14 One thunderstorm can spawn other daughter cells through the formation of a gust front Slide 15 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. Slide 16 if a dryline exists, storm development along the cold front will be minimal squall line: line of intense thunderstorms Slide 17 Mesoscale Convective Complex --a very large (~40,000 mi 2 ) organized cluster of severe thunderstorms Slide 18 MCC over Oklahoma Slide 19 MCC Slide 20 Slide 21 Imbedded in a squall line or an MCC, large, rotating thunderstorms called mesocylcones may form (1/2 of all mesocyclones produce tornadoes) Slide 22 Mesocyclone: (typically 10-30 miles wide and 70,000 feet tall!) Slide 23 Thunderstorm hazards Slide 24 Hail forms as ice crystals are swept aloft numerous time by updrafts Slide 25 Concentric rings of a hailstone Slide 26 Slide 27 Slide 28 Mircrobursta narrow, high speed downdraft (may exceed 100 mph) Slide 29 Downbursts can create straight-line winds called derechos (may be +100mph) derechos are often mistaken for tornadoes Slide 30 Destruction path of a derecho Slide 31 Derecho damage Slide 32 Lightning electrical stroke between oppositely charged particles charge separation is caused by updrafts, downdrafts Slide 33 Lightning heats the air to 50,000 F Slide 34 if you feel static electricity like this person get to a low area immediately Slide 35 Lightning Safety Slide 36 Slide 37 Thundersound of air expanding upon heating by lightning strike (sound waves travel about 1000 ft/sec)