Storms Chapter 13

Warm-up Explain the difference between climate and weather.

Thunderstorms Thunderstorm- a brief, heavy storm that consists of rain, strong winds, lightning and thunder

Thunder- the sound made by the thermal expansion of air Lightning- an electric discharge that takes place between two oppositely charged surfaces

Thunderstorms 3 conditions necessary for thunderstorms Lots of moisture in the lower atmosphere Warmer air begins to rise Atmosphere must be unstable

Stages of a Thunderstorm Cumulus stage - warm air rises upwards carrying moisture Mature stage- the precipitation falls rapidly to earth with downdrafts Dissipation- updrafts slow, storm has no more energy

Classifications of Thunderstorms Classified according to the mechanism that caused the air to rise Air-mass thunderstorms – unequal heating within one air mass 1. Sea-breeze 2. Orographic lifting Frontal thunderstorms – advancing cold fronts (strong) and advancing warm fronts (mild).

Sea Breeze Thunderstorm

Orographic Lifting/Mountain Thunderstorm Air is forced to rise due to topographic features on the Earth’s surface

Frontal Thunderstorms

Frontal Thunderstorms Advancing cold fronts Severe, forms lines of storms along front Jet stream can shear off top of cloud forming an anvil shaped cloud For us, most likely as winter turns into spring

Frontal Thunderstorms from advancing cold front

Frontal Thunderstorms Advancing warm fronts not as likely to produce frontal thunderstorms

A supercell is a self-sustaining, extremely powerful storm that has intense, rotating updrafts.

A downburst is a violent damaging thunderstorm wind concentrated in a local area.

Hail Hail is precipitation in the form of balls or lumps of ice. They form in severe storms. Indicator of tornadoes!

Severe Thunderstorm Warnings A thunderstorm with winds of 58 mph or greater Penny sized hail or larger Also contain lots of lightning Stay inside Keep off the phone Don’t take a shower or bath Stay away from windows

Tornado- destructive rotating column of air visible to the naked eye Tornadoes are classified on the Enhanced Fujita Scale which ranks them according to wind speed, duration, and path of destruction.

Tornado Warnings A tornado or funnel cloud has been detected Take shelter RIGHT AWAY!!! Get under something sturdy in your basement No basement? Go to a room that has no windows like a closet or bathroom In mobile homes, leave them and go to a storm shelter if available or lie flat in a ditch

“Tornado Alley” is located in the midwestern US where cP air mases meet mT air masses. The midwest experiences the most tornadoes in the US

April 16, 2011 Tornadoes 2:53pm - EF3 - in the city of Sanford- this is where the Lowe’s was destroyed Continued NE through Apex and Cary towards Downtown Raleigh at EF1 status Lots of damage at Shaw University Continued to N. Raleigh where it hit the mobile home park at 4:05, killing four Ended near Rolesville at 4:10 On ground for 63 miles

<- Lowes in Sanford Bottom left- houses off Capital Blvd. Below- Shaw Univ.

Path and Strength of Tornadoes

Tropical Cyclones A tropical cyclone is a large, rotating, low-pressure storm formed over warm, ocean water in the summer or fall. Types of tropical cyclones: Tropical depression – maximum winds 38 mph or less Tropical storm – maximum winds 39-73 mph. Hurricane/typhoon – maximum winds 74mph or higher.

Tropical Cyclones

Hurricane- storm over tropical oceans and whose winds are over 120 km/hr and spiral towards a low pressure center Hurricanes are classified on the Saffir-Simpson scale from 1-5 based on wind speed, air pressure and potential for property damage.

Saffir-Simpson Scale

Hurricanes Hurricane watch - hurricane conditions possible within 36 hours. Begin family's disaster plan, needed supplies, evacuation routes, etc. Hurricane warning - hurricane force winds expected within 24 hours.

Hurricanes The eye is the calm center of the storm. The eyewall is the wall of storms around the eye. Usually the strongest winds. The storm surge occurs when hurricane force winds drive water onto land. Tornadoes and heavy flooding are associated with hurricanes.