Weather. Weather or Not Uneven heating of the Earth and the rotation of the Earth causes weather systems Local weather patterns are determined by winds.

Weather

Weather or NotUneven heating of the Earth and the rotation

of the Earth causes weather systemsLocal weather patterns are determined by

winds carrying air masses◦Air masses are bodies of air with uniform

temperature and humidity conditions extending and travelling for miles in the atmosphere

◦Think of the atmosphere as a body of water that is constantly flowing/moving

◦Even if its calm at the surface, wind currents higher up may reach 180mph

Weather or NotRemember that warm air at the

surface becomes less dense (spreads out)◦Can create a huge dome of warm air

with low density◦Can be 1000 miles wide and a mile

thickCold air moves more slowly and stays

closer together (more dense)Warm low-density air raises and colder

air takes it place: convection

Weather or NotAir masses also have different

amounts of moisture content: humidity◦Depends primarily on where the air

mass formed◦Tropical waves move off the coast of

Africa during spring, summer, and fall and carried westward by air currents near the equator

Source region of an air mass can be maritime or continental; and polar or tropical

Weather or Not

  (c) continental (m) marine

(T) Tropical (cT) warm, dry (mT) warm, wet

(P) Polar (cP) cool, dry (mP) cool, wet

APEX Vidoes

Weather or NotWhen a cold front moves through, the heavier,

cool air pushes under the lighter, warm air◦As the warm air rises it begins to cool◦ If the air is humid enough, it will condense

into clouds and precipitation◦After the cold front moves in, the region will

have cooler and drier airDuring a warm front, the warm air catches up

with cold air (moving in same direction)◦Warm air rises above the cold◦Moisture condenses to form rain or snow

APEX Diagrams

Weather or NotOn a weather map symbols represent

different pressures◦H is for high-pressure area (cold air)◦Cooler, clear skies, and fair weather◦L is for low-pressure area (warm air)◦Warmer air, clouds may form, rain,

and storms

HL

Weather or NotAn occluded front forms when cold air

mass catches up with warm front◦Cold air pushes up the warm air, it

spirals counterclockwise, and cools◦Warm air isn’t felt

(occluded=hidden)

Occluded frontOccluded fronts often occur at the end

of a storm, when a cold air mass catches up with a warm front.

Stationary FrontA stationary front occurs when warm

and cold air meet but neither are moving (battle is a standoff)◦Bring days of gray skies◦Upper level winds can get them

moving again

Coriolis effect and our weatherWeather between 30ºN and 60ºN (and

30ºS and 60ºS) move from west to east◦Weather in other latitudes move

from east to west

Cloud FormationWarm humid air rises and cools to the

dewpoint◦Water condenses into microscopic

liquid or ice crystals◦Encounters dust particles

(condensation nuclei) condensing into droplets and becoming visible

Cloud TypesCirrus- high, wispy ice clouds (from

Latin meaning “curly”)Alto- from Latin meaning “middle”Stratus- low to medium height gray

clouds (from Latin meaning “spread out”); overcast sky that may result in drizzle or fog

Cumulus- low, heaped-up fluffy white clouds (from Latin meaning “heap”); form below 6000 feet

Nimbus- from Latin meaning “rain”

Cloud Types

CloudsHigh clouds, such as cirrus or cirrocumulus,

don't drop precipitation but are an indication that rain or snow is on the way.

Middle clouds, like altostratus, usually are composed mostly of water, not ice

Low clouds can mean anything from fair weather to thunderstorms

Vertical clouds span the entire spectrum and are made of both water droplets and ice crystals

APEX Videos

ThunderstormsThunderstorms require a few

atmospheric conditons:◦Moisture in the lower to middle

levels of the atmosphere◦A lifting force to cause air to begin to

rise; typically heated air near the ground

◦Unstable air (air that will continue rising once it begins rising)

ThunderstormsLightning develops from a buildup of

charges as tops of clouds become positively charge and bottoms of clouds become negatively charged

Thunder is caused by lightning heating up the air, which causes it to expand and contract quickly (contracting leads to the sound)

TornadoesRequired conditions:

◦Wind shear is the change in speed and direction of wind at different altitudes causing columns of clouds to spin

◦Sinking air pushes on end of the column toward land, while the other end rises; causes faster spinning

◦Spinning cloud joins a cloud above it, creating a funnel cloud

◦Funnel cloud touching the ground creates a tornado

Tropical CycloneLow-pressure weather systems with

circular wind motion that rotates counterclockwise in the Northern Hemisphere◦Typhoon: when thunderstorms

converge in the western Pacific or off coast of China

◦Hurricane: when storms are born off the coast of Africa and travel across the Atlantic Ocean

Tropical CyclonesConditions required:

◦Thunderstorms grow over warm ocean waters with hot, humid air

◦Air spins and rises; air within the system cools because it releases heat

◦When wind reaches 74mph, it is called a hurricane

BlizzardsWinter storms that bring low

temperatures, high winds, heavy snow, and poor visibility