1. Air Masses and Fronts

2. Definition
Air mass- huge section of the lower troposphere that have the same kind of weather (temperature and humidity) throughout.

3. Properties of Air Masses
cause changes in the weather
are classified by where they form
form over oceans and land
amount of moisture (humidity) depends
on where the mass develops.
named for source region or places of origin

4. Source Regions
Source regions for cold air masses are polar areas and are labeled P
Source regions for very cold air are arctic areas and are labeled A
Source regions for warm air are masses are tropical areas and are labeled T
Source regions over oceans are called maritime and are labeled m , they are moist
Source regions over land are called continental and are labeled c , they are dry

5. Types of air masses 5 major types of air masses mP- maritime polar
is cold and humid
brings cooler temperatures to Eastern US
Brings fog to California and western states

6. Maritime tropical mT maritime tropical holds warm moist air
in summer- brings very hot, humid weather
in winter- if this air meets with cold air mass, rain or snow will fall

7. Continental tropical
cT continental tropical
originates in tropical land areas and desert areas of SW US
are hot and dry
*Least effects the US

8. Continental polar cP continental polar originates over land in Canada
are cold and dry
causes very cold temp in the US in the winter

9. Continental arctic
cA continental arctic
very cold and dry
come from ice covered Arctic regions

12. Air masses change as they move from their source region.
they diverge from areas of high pressure and converge in areas of low pressure
are very large and take several days to pass through a region.
Fast moving air masses spend less time over any one area and bring more extreme weather

13. Fronts
boundary between air masses that have different temp. and humidity.
when two air masses meet, a front forms
an approaching front means a change in weather, almost always brings ppt.
four types of fronts
forceful lifting- when two contrasting air masses meet, the lighter warmer of the two is lifted or rises above the cooler, denser air mass. MAJOR CAUSE OF PPT in the US. (large pressure gradient)

14. Cold Front
forms when a mass of cold air meets and replaces a mass of warm air
*Moves more quickly than a warm front
cold air forces the warm air mass upward
violent storms are associated with cold front
has a steep slope
often forms a line of thunderstorms called a squall line (*lightening , hail, cumulonimbus clouds, strong wind, large pressure gradient)

18. Warm Front
forms when a mass of warm air advances into an area occupied by a cold air mass
Drizzle may accompany a warm front
hot humid, weather follows
gentle slope, *small pressure gradient, weak winds, nimbostratus clouds.

22. Occluded Front
forms when cold front overtakes a warm front (cold front travels faster then a warm front)
warm air is *pushed upward and the warm air meets cool air
weather is complex and extreme (*flash floods)

24. Stationary Front warm air mass meets a cold air mass
no movement occurs
rain may fall for days (*major flood events)

26. Cyclone An area of low pressure containing rising warm air
Convergence and forceful lifting create clouds.
cool air moves in to take the place of rising warm air
move in counterclockwise direction
rainy, stormy weather
*Closely spaced isobars *

27. Cyclone Development
A wavelike kink develops- warm air is pushing N, (warm front) cool air is pushing S (cold front)
Cold front moves more rapidly and overtakes warm front producing unstable air and cloud development
Occluded front is produced, moves *CCW, stormy, close isobars)

28. Cyclone

29. Anticyclone high pressure area containing cold dry air
clockwise direction
clear dry weather
isobars usually *farther apart , winds are weaker

30. Ways that air can be lifted:
Convective-occurs in areas where there is a large difference in heating.
Orographic- air forced to rise over mountains
Frontal- occurs along boundary between air masses.