STORMS AND SEVERE WEATHER

1. STORMS AND SEVERE WEATHER STORM: violent or severe disturbance of the atmosphere that usually creates dangerous, destructive, or unpleasant conditions on Earth’s surface.

2. Storms and Severe Weather Most storms are associated with: • High winds • Heavy precipitation • Fronts • Low air pressure of cyclonic conditions People need to be aware that storms can: • Cause loss of life • Injuries • Loss of property

3. Mid-latitude or Cyclonic Storms Caused by movement of air masses along polar fronts of the middle latitudes Results in: formation of low pressure storm systems (mid-latitude cyclones) Often associated with many thunderstorms and associated hail and tornadoes.

4. HURRICANES • An Intense low pressure system that starts as a tropical low. • Winds sustained at 74 mi/hr (120 km/hr) • Storm surge causes most of the damage. • Energy from latent heat released during condensation fuels the storm • Spin due to the CoriolisEffect • Characterized by rotating bands of precipitating clouds. • Lowest pressure is in the center of the storm (cloudless eye)

5. Hurricanes continued. • High winds can get to over 150 mi/hr • When a hurricane passes over land or cold ocean water, it loses its energy source of evaporating water and slowly dissipates. • Greatest threat is when a hurricane hits land. • In the U.S. the southern and eastern coasts are most vulnerable.

6. Hurricane Formation

8. Saffir-Simpson ScaleCategorizes hurricanes

9. THUNDERSTORMS They are heavy rainstorms accompanied by thunder and lightning from Cumulonimbus clouds A line of thunderstorms is called a squall

10. Thunderstorm lifecycle The typical lifecycle of a thunderstorm consists of three stages: towering, mature cumulus, and dissipating stage • Towering cumulus cloud indicates lifting air. • Little if any rain • Lasts about 10 minutes. • Occasional lightning

11. Mature Stage • The air continues to rise up to the tropopause, forcing the air to be spread out. • Hail, heavy rain, lightning, strong winds likely. • Lasts an average of 10 to 20 minutes .

12. Dissipating Stage • Thunderstorm dissipates and is dominated by a downdraft. • Rainfall decreases in intensity. • Three important ingredients: • Moisture • Instability • Lifting mechanism

13. Thunderstorm hazards Thunderstorms can create many hazards including flooding, hail, high winds, and lightning. In many years, more people get killed from lightning than any other weather-related cause.

14. Hail Formation

15. TORNADOES • Most violent of all storms. • By definition, a tornado is a rapidly rotating extremely low pressure funnel that hangs down from a column of air extending from a thunderstorm to the ground.

17. Tornado characteristics • Wind speeds 40 mph to 110 mph • Often travel a few miles before dissipating. • Rotate counterclockwise in NH. Opposite in SH

18. Tornado formation Before thunderstorms develop, vertical wind shear creates an invisible, horizontal spinning effect in the lower atmosphere Updraft within the thunderstorm tilts the rotating tube from horizontal to vertical. An area of rotation of few miles wide is formed within the storm. Most tornadoes form within this area of strong rotation

19. Tornado scales

20. Types of Tornadoes