Unit 6 – Hazardous Weather and Natural Disasters

Thunderstorms:• a storm with lightning and thunder. Its

produced by a cumulonimbus cloud, usually producing gusty winds, heavy rain and sometimes hail.

• Formation: Warm air rises, moisture in the air condenses (into clouds), if there is enough moisture gravity pulls it down

3 Types of Thunderstorms:• Orographic• Air Mass• Frontal

100,000 thunderstorms per year in the U.S.

Orographic• caused by air that is forced up by a mountain

or hillside.

Air Mass Thunderstorm• the result of localized convection in an unstable air mass.

Frontal Thunderstorm• Occur along the boundaries of weather fronts (e.g. cold front).

Lightning• Florida: 25.3 strikes per square mile• 1.45 million lightning strikes each year• the deadliest for lightning, 62 deaths over the

past 10 years.

Lightning(1) Negative chargesin the bottom of a cloudattract to positive chargeson the ground

Lightning(2) Negative chargesPour down to a high point where positive charges clustered

Lightning(3) When the positive charges rise up to meet the negative we see lightning and hear thunder

Thunder• The sound of rapidly expanding air• Caused when lightning heats the air

Hailstorms• Hail is precipitation in the form of large balls

or lumps of ice. • Hailstones begin as small ice particles that

grow as the hailstone moves up and down through a storm cloud picking up layers of ice 

Largest in U.S.: July 23, 2010; in Vivian, South Dakota; 8 inches, 1.94 pounds.

Tornado:• Violently rotating column of air• Most - wind speeds less than 110mph, base of

250 feet• Most extreme: Winds above 300mph, base of

2 miles• Fujita Scale – 0-5, developed by T. Theodore

Fujita• 800 per year in U.S.

Tornado formation:1. Wind at two altitudes and two speeds create a horizontal, rotating column of air

Tornado formation:2. An updraft of airspeeds, tightens, and pulls the horizontal column up

Fujita Scale:

Wind Damage

F0 73mph Light: chimneys, signs, branches

F1 73-112 Moderate: Roof shingles

F2 113-157 Considerable: Roofs torn off

Fujita Scale:

Wind DamageF3 158-206 Severe: Roofs and walls

F4 207-260 Devastating: houses leveled

F5 261-318 Incredible: Strong houses leveled; strange phenomena

Tornado Warning:A tornado has been spotted; take cover

Tornado Watch: conditions are ideal for a tornado; be prepared

Flooding: • An overflow of water that submerges

land that is usually dry• primary effects: loss of life, damage to

buildings, structures, sewerage systems, roads.

5 types: (1) Areal, (2) Riverine, (3) Estuarine, (4) Urban, (5) Catastrophic

5 types

• Areal: rain water cannot absorb into the ground

• Riverine: River banks overflow

5 types• Estuarine: Estuaries overflow

• Urban: Flooding in cities

• Catastrophic: flooding due to a dam breaking or other structure

Downbursts:Strong downdraft causing damaging winds

Two Types:• Microburst; 2.5miles or less; 5-15 minutes;

168 mph winds

• Macroburst; 2.5 miles or more; 5-30 minutes; 134 mph winds

Flash floods• rapid flooding of low-lying areas: washes, rivers, dry lakes and basins.• caused by heavy rain associated with a

severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow

Flash floods• flash floods are distinguished from a regular

flood by a timescale of less than six hours

Landslides and Mudflows

• Landslide – general term for a mass movement downhill of soil, rock, or snow

Mud flow:• mass movement of mud, water, rock, and debris caused by heavy rain or thawing

Hurricanes:• rapidly rotating storm system characterized by (1) low-pressure center, (2) strong winds, and (3) spiral arrangement of thunderstorms that produce heavy rain.

• Other names: hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone.

Hurricanes:

Need four conditions:(1) low air pressure, (2) warm temperatures, (3) moist ocean air,(4) tropical winds (near the equator).

Hurricanes:

Five stages:(1) Tropical Wave: west moving “Low”(2) Tropical disturbance: rain & thunderclouds(3) Tropical Depression: Air pressure drops,

38mph winds(4) Tropical Storm: 39-72 mph wind (named)(5) Hurricane: 73mph + winds

Saffir-Simpson Hurricane Scale: Category: Winds:• Cat-1 74-95 mph• Cat-2 96-110 mph• Cat-3 111-130 mph• Cat-4 131-155 mph• Cat-5 155 mph (rare)

Extreme cold: Temperatures drop below normal and wind speed increases

Windchill Factor: decrease in air temp-erature due to the increase in wind

Potential effects:• Frost bite: injury to body tissues due to

extreme cold (esp. nose, fingers, toes)• Hypothermia: abnormally low body

temperature (typically below 95)

Extreme heat: Temperatures rise well above normal

Potential effects:• Dehydration: Body does not have as much

water and fluids (mild, moderate, severe)• Heat stroke: a condition caused by

overheating, usually as a result of prolonged exposure to or physical exertion in high temperatures. body temperature rises to 104 F (40 C) or higher.

Potential effects (con’t):Heatstroke (con’t) untreated heatstroke can quickly damage your brain, heart, kidneys and muscles. Heatstroke requires emergency treatment.

• Heat exhaustion: condition whose symptoms may include heavy sweating, rapid pulse, and heat cramps 

Potential effects (con’t):

Sunburn: red, painful skin that feels hot to the touch — usually appears within a few hours

Second degree –blistering

Long-term – cancer; damaged skin (age spots and wrinkles)

Drought: • prolonged period of abnormally low

rainfall• result - shortage of water

Winter storms: are characterized by snowfall, rain, sleet, and ice where temperatures are below freezing.

Snowstorms: Cold storm with low temperature, sleet, snow, rain and ice formations.

Blizzards: Severe storm with strong winds, severe temperatures and heavy snow.

Ice storms: a storm of freezing rain that leaves a coating of ice.

Effects: Dangerous roads, fallen branches, downed power lines

FogFog: a thick cloud of tiny water droplets suspended in the atmosphere at or near the earth's surface that obscures or restricts visibility 

FogRadiation Fog: • forms at night under clear skies when heat is

radiated by the earth’s surface• Usually dried up after sunrise

FogAdvection Fog: • occur when moist air passes over a cool

surface• Common in near water