Download 114- Air, Masses, Fronts Notes

Air Masses, Weather, Fronts, and Lows
114
Air Mass
 An air mass is a large body of air in the lower troposphere that has similar characteristics
throughout.
 They can be large and even two or three join together to cover the entire US!
 Throughout an air mass temperatures and _______________ are uniform and dependent on their
location.
 If air stays over land for long= _________ (less vapor)
 If air stays over water for long= __________ (more vapor)
 When an air mass travels it takes with it the conditions of its origin. It can however change as it
travels due to Earth’s topography.
Types of Air Masses
• Classified according to where they _______________________.
Continental Arctic- (cA)
• Air mass originates in the arctic regions.
• Air becomes extremely cold and primarily dry
• May warm when they travel south, but will bring cold waves to regions they enter.
Continental Polar- (cP)
• Air mass originates over the inland regions of Alaska and Canada.
• A tad bit warmer than cA masses but the temperature and humidity difference is small.
• Usually just cold and dry, unless picks up moisture from waterways.
Maritime Polar-(mP)
• Air masses originate over the ocean in high latitudes.
• Cold and ________________
• Not usually as cold as cP air because of contrast in temperature between land and oceans.
• If mP cools to its dew point- fog and clouds can form or precipitation.
• Occasionally mP air from the North Atlantic bring heavy snowstorms, called nor’easters to the East
Coast in the winter and cool, clear weather to the area in the summer.
Maritime Tropical- (mT)
• Air mass originates over warm tropical __________________
• Brings up heat and humidity to the Midwest and Eastern US.
• Air contains large amount of moisture that cause thunderstorms.
Continental Tropical-(cT)
• Air masses originate over____________________ that are hot and dry.
• Often, a cT air mass originates as a maritime air mass but dries out as it passes over mountains.
• Produces heat waves in summer for US (1000F +)
• Can cause serious damage to crops
Front
• Boundaries separating opposing air masses are called ____________. Air masses don’t like to mix.
• Most common at middle latitudes such as ourselves. These fronts have southward-moving polar air
masses and northward-moving tropical air masses that meet.
• Fronts can have a wedge shape or steep slope.
• Fronts usually bring ___________________________
Kinds of Fronts
• Named for their temperatures of the advancing air mass.
– _____________ fronts
– Warm fronts
– _________________fronts
– Stationary fronts
Cold Fronts
• Boundary between quick moving cold air mass and the warmer air mass it is displacing.
• Cold air slides underneath the warm air since it is more _____________.
• Steep slopes
• The type of weather the cold front brings depends on the type of air mass it is displacing.
Warm Front
• When warm air displaces cold air, the boundary between the air masses is a warm front.
• Warm air rises above the denser cold air.
• Slope is more gradual
• High cirrus clouds followed by cirrostratus and lower/thicker stratiform clouds.
• Cirrus clouds can give warning of impending weather.
• Altostratus clouds following the cirrus and screen out the sun and the moon.
• The heavy nimbostratus clouds arrive, and steady rain or snow begins.
• Precipitation can lasts for a day or more.
• Thunderstorms can form, but are not typical.
• After front, weather __________________ up.
Occluded Fronts
• Cold fronts typically move twice as __________ as warm fronts.
• If a cold front catches up to a warm front, an occluded front forms.
• Warm air gets caught between the two colder air masses and is forced to rise.
• Causes cloudiness and precipitation.
Stationary Fronts
• If a front is ________ moving forward, it is called a stationary front.
• Warmer air rises over the denser, cold air and clouds and precipitation may form.
• If stationary front stays too long, flooding can occur.
Life Cycle of a Mid-Latitude Low
• Fronts are usually connected to mid-latitude low-pressure systems.
• Takes 12-24 hours for a low-pressure system to pass through the first two stages.
• First air pressure at a polar front drops and a wave forms on the front.
• Second warm tropical air on the east side of the front moves northward and cold polar air on the
west side moves southward.
• Third the cold front catches up to the warm front, forming an occluded front.
• The resulting storm system eventually loses energy and weakens.
Weather Associated with Pressure Systems
• If a low pressure system heading east passes to the north of you:
– As the warm front approaches from the west, cirrus clouds lead to
_________________________ clouds and produce steady snow or rain followed by drizzle.
– When the warm front passes, the temperature warms, winds shift, and the skies may slowly
clear. If humid, rain may occur.
– As the cold front approaches, it is preceded by scattered showers and possible
______________________.
– As the cold front passes, the temperature drops, winds shift again, and sky ______________.