1. Thunderstorms, Tornados, and Hurricanes

2. Thunderstorms Requirements – Warm moist air – Lifting mechanism What is the result of lifting? Most Probable Location?

3. Fig. 15.15

4. Thunderstorm formation 3 stages: 1.Cumulus Stage warm air is forced vertically upward cooling quickly, creates updrafts formation of a cumulus cloud as warm air rises and expands no precipitation occurs during this stage 2. Mature Stage condensation in uppermost reaches produces ice crystals (which can merge) Falling precipitation generates friction against updrafts – creates a downward column of movement – downdraft Failing air warms – melts some ice to produce rain other ice falls as hail Passing updrafts and downdrafts cause polarization of charges between ice particles and droplets in the clouds (causes lightning) 3. Dissipating Stage Cloud formation ends Evaporation of some of the falling rains removes energy from the system, cooling the air Cool air is more stable and prevents updrafts Light rain and dissipation of clouds

6. Lightning Lightning joins centers of opposite charges. – Top of cloud to middle- bottom – Bottom of cloud to land surface Fig. 15.17

7. Tornadoes Narrow, funnel-shaped spirals of rapidly converging and rotating air associated with thunderstorms Center around low-pressure Winds are associated with high pressure gradients – Midlatitude cyclones have gradients of 0.04 mbar/km – Hurricanes have gradients of 0.2 mbar/km – Tornados have gradients up to 100 mbar/km The higher the gradient the greater the winds

8. Tornado formation 3 stages – Early – slow air movement at the ground surface shears with rapid vertical movement, produces rolling spiral of wind – Updraft – updraft of thunderstorm pulls the spiraling air up vertically, creates mesocyclone – Tornado – rotation becomes tighter and faster, air extends downward

9. Hurricanes Characterized by high sustained winds Heavy rainfall Storm surges (elevated water levels) along coastlines Occur over the globe, but have different names – Pacific Ocean – typhoons – Indian Ocean - cyclones

10. Formation Our “hurricanes” begin as winds coming off of northern Africa

11. Formation - continued Air moves over warm water (at least 27 o C) Ocean water evaporates and subsequently condenses in the atmosphere (What has happened in terms of energy and temperature?) Warm humid air continues to be drawn into the air mass and is forced upwards (creating a greater pressure gradient). Prevailing winds create cyclonic rotation (counterclockwise)

12. Formation - continued Lowest pressure develops at the center where air is being forced upwards Continued evaporation of warm waters increases the movement of air and strengthens the storm

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14. Fig. 15.23

15. Daily Question Using a Venn Diagram, compare and contrast midlatitude cyclones, tornadoes, and hurricanes. Provide a minimum of 7 items. Tornadoes Midlatidude cyclones Hurricanes 1)Destructive winds 2)Rain 3)Cold front advances on a warm front 4)Form off of Africa 5)Center around low pressure 6)Counter clockwise air movement 7)Associated with thunderstorms 8)Short duration 9)Require warm water 10) form over land 11)Geographically affects a large area 12)Moves west to east 5, 6, 7 8 1 2 3 4 9 10 11 12