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 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 Not Remember 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 thick Cold air moves more slowly and stays closer together (more dense) Warm low-density air raises and colder air takes it place: convection

Weather or Not Air 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 APEX Vidoes (c) continental (m) marine (T) Tropical   (c) continental (m) marine (T) Tropical (cT) warm, dry (mT) warm, wet (P) Polar (cP) cool, dry (mP) cool, wet APEX Vidoes

Weather or Not When 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 air During 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 Not On 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 H L

Weather or Not An 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 front Occluded fronts often occur at the end of a storm, when a cold air mass catches up with a warm front.

Stationary Front A 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 weather Weather between 30ºN and 60ºN (and 30ºS and 60ºS) move from west to east Weather in other latitudes move from east to west

Cloud Formation Warm 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 Types Cirrus- 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

Clouds High 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

Thunderstorms Thunderstorms 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)

Thunderstorms Lightning 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)

Tornadoes Required 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 Cyclone Low-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 Cyclones Conditions 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

Blizzards Winter storms that bring low temperatures, high winds, heavy snow, and poor visibility