ATMOCN 100 Chapters 10 and 11

Isotherm

Isotherm

line of constant temperature

Isobar

line of constant pressure

Supercell thunderstorm

intense storm with single, violently rotating updraft = commonly produces severe weather = can produce the largest hail

Spring

season with peak tornado activity in U.S.

Air mass thunderstorm

small, scattered, short-lived, and far from fronts = air mass thunderstorm = rarely severe

MCC = mesoscale convective complex

large circular convective weather system = can produce hail, high winds, destructive flooding, and tornadoes

Triggers to produce rising motion in support of thunderstorm development

mountain slopes, weather fronts, turbulent eddies, unequal surface heating, upper-level divergence, shallow boundaries of converging surface wind

Vertical wind shear

change in wind direction or speed with height

Types of vertical wind shear

Directional and speed shear

Directional shear

wind direction changing with height

Speed shear

wind speed increasing with height

Thunderstorms

common over tropical land masses worldwide

Florida = most thunderstorms in U.S.

due to convergence of sea breezes across peninsula

Moisture from the Gulf of Mexico

supports thunderstorm activity across the southeast US

Colorado

most hail in U.S.

Why does Colorado have the most hail?

cool column of air to the east of the Rockies supports hail growth

Stages of thunderstorm development

cumulus stage (birth/growth), mature stage (peak), dissipating stage (decay)

Overshooting tops of cumulonimbus clouds sometimes

pass through the tropopause (top of troposphere).

Severe Thunderstorm Watch

chance of strong wind, hail, or tornado

Derecho

strong damaging straight-line winds along a path of 400+ km

When do derechos happen?

usually in evening-night

July 1995 derecho

straight line winds across NY Adirondack Mountains

Squall line = type of multicell thunderstorm

narrow line of thunderstorms = 10 km wide = 100s km long = capable of producing severe weather along much of its length

Stepped leader

channel of negative charges traveling to the ground

Upward leader

streamer = currents of positive charge moving upwards from the ground, up elevated objects like trees

Return stroke

visible part of a lightning stroke

Where do return strokes go?

follows the path of the stepped leader

How common is cloud-to-ground lightning?

only about 20% of total lightning flashes

Typical electrical charge in a cumulonimbus cloud

positive on top, negative on bottom

When are U.S. tornadoes are most frequent?

May

When are U.S. tornadoes are least frequent?

January.

Do tornadoes form ahead or behind cold fronts?

ahead

What country has the most tornadoes in the world?

United States

Funnel cloud

rotating column that does not touch the ground

Tornado Alley

in central U.S. = where tornadoes are most frequent

most tornadoes in U.S.

Kansas

How many tornadoes rotate counterclockwise?

98%

What happens if the tornado sirens go off?

seek shelter indoors in a storm shelter, basement, or saferoom.

Enhanced Fujita Scale

describes tornado intensity by observing damage caused by the tornado

EF0

weakest, most common

EF5

most violent, least common

Saffir-Simpson hurricane wind scale

relates a hurricane's winds to the possible damage it is capable of inflicting to a coastal region = cat 1 to 5

Category 3-5

major hurricane

Tropics

between 23N (Tropic of Cancer) and 23S (Tropic of Capricorn)

Tropic of Cancer

23N

Tropic of Capricorn

23S

Hurricane

sustained winds of at least 74 miles/hour = also called a typhoon

Where do hurricanes not form?

equator because the Coriolis force is negligible.

Hurricane eye

calm winds = clear skies = lowest air pressure = sinking motion

Eye wall

wall of dense thunderstorms around the hurricane eye = strong rising motion = heaviest rains and strongest winds

Spiral rain bands

spiral bands of rain-producing clouds that swirl in towards and wrap around the eye

Tropical easterly waves

migratory wavelike disturbances in the tropical easterlies = can originate over sub-Saharan Africa and turn into Atlantic hurricanes

Tropical Atlantic hurricane season

begins in June, peaks in September, ends in November

States vulnerable to being hit by a tropical storm/hurricane

Florida, Texas, North Carolina, Louisiana, and South Carolina

Storm surge

aspect of hurricanes that causes the most loss of lives and damage

What causes a storm surge?

abnormal rise of the sea along a shore primarily due to the winds of a storm

Stages of Hurricane development

tropical disturbance, tropical depression, tropical storm, hurricane

Hurricane watch

hurricane conditions are possible

Hurricane warning

hurricane conditions are expected

Butterfly effect

tiny fluctuation in wind can affect the global circulation

Favorable conditions for hurricanes

warm surface waters, high humidity throughout troposphere, and weak wind shear

Where do hurricanes strengthen?

over tropical oceans

Where are hurricanes weaker?

over land

Latent heat from evaporation of ocean water

provides fuel to hurricanes.

What does the enhanced fujitia scale apply to?

Tornadoes

Which type of front is most capable of producing tornadoes?

Cold front

What are the weather conditions like in the eye of a hurricane?

Calm winds

What aspect of a hurricane is most damaging?

Storm surge

If you are a national weather service forecaster, which is true?

Large hail is possible, so you issue a severe thunderstorm watch

Which is true about thunderstorms?

Air mass thunderstorms are small, short-lived, and away from fronts

What is true about June for the North Atlantic hurricane season?

The season begins

Which is the peak stage of thunderstorm development?

Mature stage

Which is most likely to produce severe tornadoes and hail?

Supercell thunderstorm

During which month are north atlantic hurricanes most common?

September

How does ocean evaporation affect a tropical storm?

Provides field to the system to strengthen it

___ often form over Africa and can atler turn into hurricanes over the Atlantic ocean?

Tropical easterly winds

Which development stage occurs before tropical depression?

Tropical disturbance

Which is true about Lightning?

The return stroke is the aspect of lightning that we see

Which is true? (a) Hurricanes form from tropical easterly waves. (b) Hurricanes in the North Atlantic turn clockwise. (c) Hurricanes strengthen over cold ocean waters.

Hurricanes form from tropical easterly waves

What type of thunderstorm consists of a narrow line of thunderstorms that may be 10 km wide but 100s of kilometers long? (a) MCC (b) Air mass thunderstorm (c) Squall line

Squall line

What boundary do the overshooting tops of some cumulonimbus clouds sometimes pass through? (a) Thermopause (b) Stratopause (c) Tropopause

Tropopause