Download Air Masses

Air Masses and Fronts
Definition
Air mass- huge section of the
lower troposphere that have the
same kind of weather
(temperature and humidity)
throughout.
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
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
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
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
Continental tropical
cT continental tropical
originates in tropical land
areas and desert areas of SW
US
are hot and dry
*Least effects the US
Continental polar
cP continental
polar
originates over
land in Canada
are cold and dry
causes very cold
temp in the US in
the winter
Continental arctic
cA continental arctic
very cold and dry
come from ice covered Arctic
regions
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
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)
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)
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.
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)
Stationary Front
warm air mass meets a cold air
mass
no movement occurs
rain may fall for days (*major
flood events)
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
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)
Cyclone
Anticyclone
high pressure area
containing cold dry
air
clockwise direction
clear dry weather
isobars usually
*farther apart ,
winds are weaker
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.