FRONTS AND AIR MASSES(also the 6 important cloud types)

Cumulus Clouds• Description – Thick and puffy and usually white

• Altitude – usually below 2000m

• Loc. in troposphere – low

• Composition – Water droplets

• Name meaning – heap

• Weather – fair weather

Stratus Clouds• Description – Thin, flat, gray, and often look a single sheet of clouds

• Altitude – usually less than 2000m

• Loc. in troposphere – low

• Composition – water droplets

• Name meaning – layer

• Weather – light rain/drizzle

Cirrus• Description – Thin, white and feathery

• Altitude – above 6000m

• Loc. in troposphere – high

• Composition – ice crystals

• Name meaning – curl

• Weather – none

Cumulonimbus Clouds• Description – large and towering, white to dark gray, flat anvil-shaped

top

• Altitude – from 1000m – 12000m

• Loc. in troposphere – low, extending high

• Composition – water droplets, ice crystals at high altitudes

• Name meaning – cumulus=heap, nimbus=rain

• Weather – rain, hail, thunderstorms, tornadoes

Nimbostratus Clouds• Description – dark, thick, and gray

• Altitude – from 0m-3000m

• Loc. in troposphere – low to middle

• Composition – usually water droplets, but may have ice crystals

• Name meaning – nimbus=rain, stratus=layer

• Weather – rain/snow

Fog• Description – thick, gray

• Altitude – ground level

• Loc. in troposphere – low

• Composition – water droplets

Air Masses• An air mass is a large volume of air in which the

temperature and moisture content are nearly the same throughout

• When air stays over a region for many days, the air gradually takes on the characteristics of the land or water beneath it

• When they move, they bring these characteristics with it• Air masses can change temperature and humidity when

they move to a new area

Fronts

• A front is a boundary between 2 air masses• Fronts are formed when 1 air mass runs into another

air mass• Density differences between the 2 air masses keep them

from mixing• Cool air masses are denser than warm air masses• The type of front that forms depends upon the

temperature and moisture content of the air masses, and how they move in relation to each other

• They cause weather changes as they pass

Cold Front

• Marked on a map with a blue line and blue triangles pointing towards the warm air.

• Cold air mass pushes the warm air mass up• If the warm air mass is moist, clouds will form• Associated with cumulus and cumulonimbus clouds • Produce short-lived showers, thunderstorms or heavy

snow.• Cooler, drier weather follows a cold front

Cold Front

Warm Front

• Marked on a map by a red line with red semi-circles pointed towards the cool air

• A warm air mass rises over a retreating cold air mass causing its moisture to condense into clouds

• Very commonly produce stratus type clouds• Overcast skies, fog, and light rain or snow• May also produce cirrus, cumulonimbus, and stratocumulus

clouds• Followed by warm clear weather

Warm Front

Short Video on Cold and Warm Fronts

https://www.youtube.com/watch?v=huKYKykjcm0

Stationary Front

• Marked by alternating blue lines & blue triangles (pointed in the direction of the warmer air) and red lines & red semi-circles (pointed in the direction of the cooler air)

• A cold air mass and a warm air mass are touching, but not enough wind for either to move

• Not much movement along the front • Can be clear, but can cause many days of bad weather

Stationary Front

Low Pressure System• Air in a low pressure area rises• As the air rises, it cools, reaches its dew point, and

clouds form• Low pressure systems often occur near the boundary

between warm and cold air masses• Causes rainy conditions• Counter-clockwise motion• Remember Low pressure means Lousy weather

High Pressure System• Air is sinking and moving outward• Sinking air is denser, so the pressure is higher• As the air sinks, it warms and relative humidity drops• Clouds often disappear• High pressure systems usually bring clear skies and

gentle breezes• Clockwise motion• Remember High pressure is Happy weather

Fronts on the Map

Air Masses (air masses activity)

Types of Air Masses• Continental Polar, “cold and dry”

• Originates closer to the Poles over land-locked regions.

• Continental Tropical, “warm and dry”• Originates closer to the Tropics over land-

locked regions.

• Maritime Polar, “cold and damp”• Originates closer to the Poles over water.

• Maritime Tropical, “warm and humid”• Originates closer to the Tropics over

water.