STORMS AND SEVERE WEATHER STORM violent or severe

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

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

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.

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 Coriolis Effect – Characterized by rotating bands of precipitating clouds. – Lowest pressure is in the center of the storm (cloudless eye)

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.

Hurricane Formation

Saffir-Simpson Scale Categorizes hurricanes

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

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

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.

Dissipating Stage • Thunderstorm dissipates and is dominated by a downdraft. • Rainfall decreases in intensity. • Three important ingredients: 1. Moisture 2. Instability 3. Lifting mechanism

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.

Hail Formation

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.

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

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

Tornado scales

Types of Tornadoes