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Average annual # of days with thunderstorms Deaths from Natural Hazards in the US.

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Presentation on theme: "Average annual # of days with thunderstorms Deaths from Natural Hazards in the US."— Presentation transcript:

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2 Average annual # of days with thunderstorms

3 Deaths from Natural Hazards in the US

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

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

6 Life Cycle of a Thunderstorm 1. Cumulus stage—water vapor is moved aloft by updrafts; vertical cumulus development

7 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

8 3. Dissipating stage—downdrafts dominate and moisture input from surface ceases

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10 “Anvil head”

11 Help me!

12 A roll cloud may signal the advance of a gust front

13 In some areas, the break up of a temperature inversion in the afternoon can lead to thunderstorm development

14 One thunderstorm can spawn other ‘daughter’ cells through the formation of a gust front

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.

16 if a dryline exists, storm development along the cold front will be minimal squall line: line of intense thunderstorms

17 Mesoscale Convective Complex— --a very large (~40,000 mi 2 ) organized cluster of severe thunderstorms

18 MCC over Oklahoma

19 MCC

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21 Imbedded in a squall line or an MCC, large, rotating thunderstorms called mesocylcones may form (1/2 of all mesocyclones produce tornadoes)

22 Mesocyclone: (typically 10-30 miles wide and 70,000 feet tall!)

23 Thunderstorm hazards

24 Hail forms as ice crystals are swept aloft numerous time by updrafts

25 Concentric rings of a hailstone

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28 Mircroburst—a narrow, high speed downdraft (may exceed 100 mph)

29 Downbursts can create straight-line winds called derechos (may be +100mph) derechos are often mistaken for tornadoes

30 Destruction path of a derecho

31 Derecho damage

32 Lightning –electrical stroke between oppositely charged particles charge separation is caused by updrafts, downdrafts

33 Lightning heats the air to 50,000º F

34 if you feel static electricity like this person get to a low area immediately

35 Lightning Safety

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37 Thunder—sound of air expanding upon heating by lightning strike (sound waves travel about 1000 ft/sec)


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