Transcript Weather Patterns

Weather Patterns
Air masses
Changes in the weather are caused
by movements of large bodies of
air called air masses. Air masses
usually cover thousands of square
kilometers. The properties of an
air mass are nearly the same
throughout the air mass.
The 4 major types of air masses
that affect the weather in the
United States are:
1. Maritime Tropical- forms over the
ocean, near the equator, warm moist
air.
2. Maritime Polar- forms over the
Pacific Ocean and North Atlantic. Brings
fog to California. Cold, moist air.
3. Continental Tropical- forms
over land in Mexico, brings dry, hot
air.
4. Continental Polar- forms over
land in Northern Canada, brings
cold, dry air.
Fronts
When 2 air
masses that have
different
properties meet,
they do not mix
readily. Instead a
boundary called a
front forms.
There are 4
different types of
fronts.
1. Cold Front: A cold air mass that
replaces a warm air mass
(draw the blue one here-#1)
2. Warm Front: Warm air mass replaces a
cold air mass
(draw the red one here-#2)
3. Occluded Front: Cold front overtakes
a warm front.
(draw the purple one here-#4)
4. Stationary Front: Warm air mass
meets a cold air mass and no
movement occurs. Rain may fall for
several days.
(draw the red & blue one here- #3)
Diagram of a cold front
Storms
A storm is a violent disturbance in the
atmosphere. When 2 different fronts collide,
rainstorms or snowstorms form. When a
warm front moves in and meets a cold front,
heavy nimbostratus clouds produce heavy rain
or snowfall. Thunderstorms are heavy
rainstorms accompanied by thunder and
lightning.
Lightning is a sudden discharge or spark of
electricity between two clouds or between a
cloud and the ground. This spark forms
because areas in the clouds build up with
positive and negative charges. Thunder is the
sudden expansion of the air when lightning
strikes.
A hurricane is a powerful cyclone (A low
pressure area containing rising warm air) that
forms over tropical oceans. Hurricanes that
form over the Pacific Ocean are called
typhoons. In a hurricane, there is a calm
center called the eye of the hurricane.
A tornado is a whirling funnel shaped cloud that
can be incredibly destructive. The air pressure
at the bottom of a cumulonimbus funnel cloud
is very low. When this low pressure area
touches the ground, the tornado acts as a
vacuum. Scientists are not sure how tornados
form. Tornadoes are very common in the
Great Plains of the United States. This area is
referred to as Tornado Alley.
THE END