Severe Weather
Thunderstorms & Lightning
Thunderstorm Development • Thunderstorms need: • moisture • warm air • lifting capability (fronts, sea breeze, mountains) • Cumulus clouds (white, puffy) form from lifting air and develop into cumulonimbus clouds
Lightning • Results from buildup and discharge of electrical energy between + and – areas within a rising cloud • Lightning rapidly heats the surrounding air, causing a shock wave we hear as thunder • Three types: • Within cloud • Between cloud • Cloud-to-ground
Thunderstorm Formation Lightning Formation
HURRICANES
Hurricane Life Cycle • Start as pre-existing low pressure systems, called tropical waves, over warm ocean waters • Evaporating ocean waters and heated air rise and develop thunderstorms • Storms begin to swirl around the low pressure center due to the Coriolis Effect (spinning of the Earth)
Hurricane Structure • Eye – sinking air in the center of the storm forms a calm, cloud-free eye that can be 20 – 40 miles across • Eyewall – dense thunderstorms surrounding the eye; strongest winds • Rainbands – thunderstorms and clouds that spiral outward from the center; spin counter-clockwise in the northern hemisphere
Hurricane Stages • Tropical Depression – strengthening tropical wave; winds less than 34 mph • Tropical Storm – continued strengthening; winds between 35 – 73 mph; named • Hurricane – when winds reach 74 mph; eye forms • Hurricanes lose energy when they make landfall, or emerge into colder waters
Notice how this hurricane got worse over the dark red (warmer water) and finally died when it got over the colder water.
How Do You Measure a Hurricane? • Hurricanes are measured by their speed and it is split into categories • The categories range from one to five, with one being the weakest and five being the strongest • The classification of hurricane systems is called the Safir-Simpson Hurricane Scale
Safir-Simpson Hurricane Scale Category One 74 to 95 MPH Category Two 96 to 110 MPH Category Three 111 to 130 MPH Category Four 131 to 155 MPH Category Five Winds greater than 155 MPH Note: Hurricanes of Category Three or above are considered major hurricanes.
A storm surge is the change in sea level produced by wind pushing the water up onto the shore. It is the MOST damaging part of a hurricane.
Important Hurricane Terms • A Hurricane Watchoccurs when a hurricane is possible within 36 hours • The storm is being tracked to predict where it may hit • A Hurricane Warningis issued when the storm is expected to hit within 24 hours • Evacuation may be needed
Hurricane Safety Tips • Know if the location you are in is a safe zone or whether evacuation may be needed • Protect windows and glass with plywood • Turn off utilities • Have a supply kit including first aid, water, canned goods, battery powered radio, blankets, etc. • After evacuation, do not return until it has been declared safe
TORNADOES
What is a Tornado? • A tornado is a violently rotating column of air extending between, and in contact with, a cloud and the surface of the earth • Tornadoes can come one at a time or in clusters • They can also vary in size, length, width, direction of travel, and speed
Tornado Formation • Changing wind direction and increased wind speed prior to a thunderstorm creates an invisible, horizontal spinning effect in the lower atmosphere • Rising warm air within the thunderstorm tilts the spinning air upward into the storm • The vertical spinning column of air begins to rotate the thunderstorm, and a tornado soon forms
Formation Waterspout
The Enhanced Fujita Scale EF 0 65 to 85 MPH EF 1 86 to 110 MPH EF 2 111 to 135 MPH EF 3 136 to 165 MPH EF 4 166 to 200 MPH EF 5 Over 200 MPH
How Do You Measure a Tornado? • Since February 1, 2008 tornadoes have been measured based on the Enhanced Fujita Scale (EF) • This scale helps determine the speed of a tornado from weakest to strongest
Tornado Facts • Waterspouts – tornadoes that form over water; usually weaker than land tornadoes • Tornadoes can be transparent, and only appear when dust and debris get picked up into the funnel • Tornadoes can occur anywhere on Earth, but are most common in “Tornado Alley” in the central United States
Tornado Safety • Tornado Watch – conditions are right for tornado development • Tornado Warning – one has been sighted or indicated in the area; take shelter • If inside – stay away from windows, get in a central room or basement • If outside – seek shelter, get out of cars and get on the ground or in a ditch
More Severe Weather • Flash Floods • Heavy rainfall over a short period of time; causes most fatalities during thunderstorms • Hail • Strong vertical winds within thunderstorm clouds (updrafts) carry rain drops to heights where they freeze; once they get too heavy they fall to the ground
SUN SAFETY • The Sun’s ultraviolet radiation can cause health risks, including skin cancer • Surfaces like snow, water, and beach sand can double the effect of UV radiation
HOW TO PROTECT YOURSELF
