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 ScaleCategory One 74 to 95 MPHCategory Two 96 to 110 MPHCategory Three 111 to 130 MPHCategory Four 131 to 155 MPHCategory Five Winds greater

then 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 Watch occurs when a hurricane is possible within 36 hours

The storm is being tracked to predict where it may hit

A Hurricane Warning is issued when it 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 ScaleEF 0 65 to 85 MPHEF 1 86 to 110

MPHEF 2 111 to 135 MPHEF 3 136 to 165 MPHEF 4 166 to 200 MPHEF 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