unit 6 hazardous weather
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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
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