FRONTS
http://www.phschool.com/atschool/phsciexp/active_art/weather_fronts/
The movement of air masses is determined by the prevailing winds
and upper air currents This causes most local weather condition
changes Reminder: Low pressure system = Lousy weather High pressure
system = fair weather High pressure system = fair weather
Slide 2
FRONT An area where two air masses with different temperatures
and densities collide but do not mix. This collision causes storms
and changeable weather. There are 4 types of fronts, see esrt. page
13 for symbols.
Slide 3
COLD FRONT Occurs when a rapidly moving cold air mass runs into
a slowly moving warm air mass. Dense cold air wedges under warmer
air and pushes it upward. Warm air rises, cools and condenses.
Passage of a cold front means rising barometric pressure = High
Pressure system Towering cumulus and cumulonimbus clouds form from
the drops of water produced by the rapid rise of warm air.
Slide 4
Weather Conditions: Cold fronts move quickly, therefore they
can cause abrupt weather changes. Strong winds and severe
thunderstorms often occur. If enough water is in the air, heavy
rain or snow can occur. If little water in the air, then there are
only cloudy skies.
Slide 5
Cold front
Slide 6
Slide 7
WARM FRONT Occurs when a slow moving warm air mass collides
with a slowly moving cold air mass. Cold air is more dense so warm
air rises over the cold air. The warm air rises up and over the air
mass it is replacing The warm air rises up and over the air mass it
is replacing Slower moving than a cold front., Take a day or two to
pass over. Slower moving than a cold front., Take a day or two to
pass over. As the front passes, the temperature increases slowly As
the front passes, the temperature increases slowly Passage of a
warm front means sinking barometric pressure = low pressure system
Passage of a warm front means sinking barometric pressure = low
pressure system
Slide 8
Weather Conditions Clouds, storms and rain often occur. If the
warm air is dry, clouds form. If the warm air is humid, showers
form along the boundary If the warm air is humid, showers form
along the boundary The rising air may lead to thick layered clouds
and gentle but long lasting precipitation Light rain or snow for
long periods
Slide 9
Warm Front
Slide 10
Slide 11
STATIONARY FRONT When the power of the cold and warm air are
the same, neither the cold and warm air masses do not have enough
force to move the other. When the power of the cold and warm air
are the same, neither the cold and warm air masses do not have
enough force to move the other. Where the warm and cool air meet,
water vapor in the warm air condenses into rain, snow, fog or
clouds. Where the warm and cool air meet, water vapor in the warm
air condenses into rain, snow, fog or clouds. Can remain in one
location and keep skies cloudy for hours to days. Can remain in one
location and keep skies cloudy for hours to days. Direction of the
movement is difficult to predict with a stationary front. *** If
the stationary front advances towards the side of the half circles,
it becomes a warm front. *** If the stationary front advances
towards the side of the blue triangles, it becomes a cold
front.
Slide 12
STATIONARY FRONT
Slide 13
OCCLUDED FRONT Cold fronts move faster than warm fronts
resulting in the cold front overtaking the warm front A warm air
mass is caught between two cooler air masses The less dense warm
air mass is pushed up. The air below becomes cooler and the warm
air mass is cut off from the ground (aka occluded) Body of warm air
is held aloft by two cooler air masses merging beneath
Slide 14
Weather Conditions: Warm air cools and water vapor condenses,
resulting in cloudy and rainy weather or snow. Warm air cools and
water vapor condenses, resulting in cloudy and rainy weather or
snow. Often associated with severe weather conditions Often
associated with severe weather conditions ** The warm air/cold air
interface is isolated above surface, a change in temp may not be
noticed on the ground.