1. Thunderstorms and Tornadoes Last Lecture: We looked at severe weather events in the lower latitudes Principal weather event is the formation and movement of Tropical Cyclones Today: Today we will look at severe weather in the mid- latitudes Most severe weather is related to thunderstorms Significant convection and precipitation Very strong winds Produces thunder and lightning Can also initiate tornados - most intense wind events on planet

2. Thunderstorms and Tornadoes Thunderstorms Cells of local, intense convection resulting in the formation of cumulonimbus clouds, heavy rainfall, lightning and occasionally hail and tornados

3. Air Mass Thunderstorms Isolated storms generated by daytime heating of land surface Convection Cell

4. Thunderstorms and Tornadoes Severe Thunderstorms Thunderstorms with high winds, hail and possibly tornados

5. Mesoscale Convective System Long-lived, intense cluster of convection cells Mesoscale Convective Complexes Large circular complex of thunderstorms active during the night

6. Squall line Line of severe thunderstorms and very strong winds

7. Dry line Boundary between hot, dry air and warm, moist air, which tends to form squall line

8. Lightning electrical discharge producing light from cloud to cloud or cloud to ground Thunder sound of rapid expansion & cooling of superheated air around a lightning bolt

9. Charge Separation Difference in charge between cloud top and bottom

10. Lightning stroke Complex series of processes which produce electrical discharge between cloud and ground Leader Channel of ionized air along which lightning stroke propagates

11. Tornado Small, intense cyclonic storm characterized by a funnel descending from mesocyclone

12. Tornado Dynamics Wind Shear Convection

13. Thunderstorms and Tornadoes Tornado Dynamics con’t. Mesocyclone Tornado

14. Thunderstorms and Tornadoes Tornado Structure

15. Weather Conditions during Formation Cold front provides Wind Shear Squall Line provides Convection

16. Thunderstorms and Tornadoes “Tornado Alley” Region of the United States with high frequency of tornado occurrence

17. Fujita Scale Measure of strength of tornado based upon severity of damage left behind

18. Detection of Tornado Vortex Signature using Radar Hook Echo