CCHS Meteorology Brown

Lifting Mechanisms Air Masses and Weather Fronts Air Pressure and Wind

Air Mass

a body of air that has about the same temperature and moisture throughout

air pressure

is the force that air exerts per unit area and is caused by the weight of the air above a surface

anticyclone

a high pressure system characterized by an outward, clockwise flow of air in the northern hemisphere

Arctic (A)

added to the name of an air mass originating anywhere from 90-66 degrees latitude, this air mass will be extra cold

Cold Front

a boundary between a cold and warm air mass when the cold air mass takes over an area. The cold air pushes up the less dense warm air. Temperature goes from higher to lower as front passes. Cumulonimbus clouds, heavy rain and severe weather are common along the steep front boundary.

Continental (c)

added to the name of an air mass that forms over the land. The air mass will be dry.

Coriolis effect

the rotation of the earth which causes the wind to bend to the right of its intended flow from high to low perpendicular to isobars

cyclone

a low pressure system characterized by an inward and counterclockwise flow of air in the northern hemisphere. Tornadoes, hurricanes and winter storms like Nor'easters are all types of cyclones.

Front

a boundary between two air masses of different density, moisture, or temperature

isobar

a line on a weather map that joins points having the same barometric pressure. The closer they are the faster the wind.

Land breeze

local wind blowing from the land toward the ocean. Forms during the night due to land losing more heat making air above land higher pressure than over water.

Maritime (m)

added to the name of an air mass that forms over the ocean. The air mass will be humid.

Mid-latitude cyclone

an area of low pressure that has counter-clockwise rotating winds and undergoes cyclogenesis giving it a warm and cold front coming out the south south side and ending with an occluded front. Brings us most of our precipitation and weather changes. Nor'easter, bomb cyclones are an examples of a mid-latitude cyclone.

monsoon

A seasonal reversal of wind direction associated with large continents (especially Asia) caused by differential heating of land vs. water

Occluded Front

a front where a warm air mass is caught between and above two colder air masses, which occurs when a cold front catches up to a warm front. It brings cool temperatures and long periods of rain and snow

Polar (P)

added to the name of an air mass that originates anywhere from 65-33 degrees latitude. The air mass will be cold.

sea breeze

A local wind blowing from the ocean toward the land during the afternoon in costal areas formed due to differential heating of land vs. water and associated pressure gradient

Stationary Front

A boundary between two air masses that is not moving, no change in temperature because neither is moving in. Usually results in cloudy weather and mild temperatures.

Tropical (T)

Part of air mass classification scheme that denotes an air mass that forms over warm regions to our south. Suggests the air mass will be warm.

warm front

a front between a warm and cold air mass in which the warm air mass is replacing the cold at the surface. As warm air lifts in a gentle slope over cold air it brings a typical pattern of cirrus, cirrostratus/cirrocumulus, altostratus, stratus and finally nimbostratus drizzly rain followed by warm and clear weather. Sleet and freezing rain associated with this front in the winter.

Wind

Horizontal movement of air from high to low in an attempt to equalize air pressure

rain shadow

a region with dry conditions found on the leeward side of a mountain range as a result of humid winds from the ocean causing precipitation on the windward side

windward

side of mountain that faces the wind and receives most of the rain

Leeward

The side of a mountain range that faces away from the oncoming wind and receives very little rain.

prevailing winds

winds that blow in the same direction over large areas of Earth

orographic lifting

cloud formation that occurs when warm moist air is forced to rise up the side of a mountain

frontal wedging

lifting of air resulting when cool air acts as a barrier over which warmer, lighter air will rise

convergence

when air flows in from opposite directions, collides, and rises

Local Convective Lifting

Localized warmer pockets of air rise because of unequal surface heating

jet stream

a high-speed high-altitude air stream blowing from west to east near the top of the troposphere

pressure gradient

change in pressure over distance

altitude

Elevation above sea level

tornado

a localized and violently destructive windstorm occurring over land characterized by a funnel-shaped cloud extending toward the ground, that rotates around a low pressure system.

hurricane

A severe storm that develops over tropical oceans and whose strong winds of more than 120 km/h spiral in toward the intensely low-pressure storm center

typhoon

A tropical cyclone, like a hurricane, that occurs in the western Pacific ocean

rain

water falling in drops from vapor condensed in the atmosphere

freezing rain

rain that freezes after it hits the ground or other cold surfaces

sleet

forms when rain falls through a layer of freezing air.

snow

form of precipitation that falls through cold air and never melts

map view

a map drawn as if you were looking down on an area from above Earth's surface

cross sectional view

side view (ex. cutting a cake, able to see its layers)