FRONTS AND STORMS

Weather Changes as air masses move

Air Mass

Forms when air sits for many days Large volume

of air

Same temperature and humidity in different locations

At the same altitude

Covers thousands of miles

As air mass moves

Earth is cold

Air is cold

Earth is wet

Air is moist

It brings its Temperature and moisture to new location

Air masses are named according to the area where they form

First part of the Name:

Continental – means the air mass formed over land, air is dry

Maritime – means the air mass formed over water, air is moist

Second part of the name:

Tropical – means the air mass formed near the equator, air becomes warm, gains energy from land or water

Polar – means the air mass formed far from the equator, air becomes cool, loses energy to the cold land or water

How do air masses move ?

Air masses can travel away from regions where they form.

They move with the global pattern of winds. In most the United States, air masses generally move from west to east.

They may move along with the jet stream. In more complex and changing patterns

They bring their temperature and moisture to their new location.

Can cause weather to change

FRONTS

Boundary between air masses Clouds form Weather

becomes cloudy or stormy

Warm Front

Moves slow, brings many hours of rain or snow. After front passes air is warmer

Warm air moves up and over a mass of denser and colder air

Produces cloud covered skies high cirrus clouds

Symbol

Cold Front

Moves quickly, very steep

After front passes air is cooler and often very clear

Produces cumulonimbus clouds and precipitation

Brief, heavy storms are likely Cold dense air is moved

forward, warmer air is pushed upward

Symbol

Stationary Front

Symbol

Occurs when air masses meet, or when cold or warm fronts stop moving, boundary is in same locationClouds

cover the sky for days at a time

May become a warm or cold front, depends on which air is pushed down

High Pressure System

Large and change slowly

Water droplets evaporate, so clouds often disappear

Calm air or gentle breezes

Generally brings clear skies

Is formed when air moves all the way around a high pressure center

Low Pressure System

Air moves inward toward the low pressure and then up to higher altitudes

Is a large weather system that surrounds a center of low pressure

Air moves faster

Produces stormy weather

Northern hemisphere air circles in a counter clockwise direction

They often happen along the boundary of warm and cold air masses

Hurricanes

Warm water makes it bigger and stronger

Land or cool water makes them weak and lose energy

Tropical Low Pressure system

Winds blowing at speeds of at least 120Km/Hr.

Formed over the Indian Ocean or Western Pacific called Typhoons or Cyclones

Move westward with the trade winds

Strike b/w August and October

Low – Pressure Systems can become storms

FORMATION OF HURRICANES

Bands of heavy clouds and rain spiral inward toward

the eye

Center is called the EYE of the hurricane

The center is calm because the air moves downward

Air moves quickly around and upward

Tall ring of cumulonimbus clouds form the eye wall

The ring produces heavy rain and tremendous winds

EFFECTS OF HURRICANES

Strong winds

Heavy rain

May produce Tornadoes

Rivers may overflow and flood nearby areas

Can create a storm surge

STORM SURGE

Destructive and deadly

Huge mass of ocean water

Produces LARGE WAVES that can move back up

rivers and flood their shores

THUNDERSTORMS

ARE STORMS WITH

Lightning Thunder

VERTICAL AIR MOTION CAN CAUSE SEVERE STORMS

FORMATION OF THUNDERSTORMS

Rising humid air forms a cumulus cloud which eventually forms into cumulonimbus cloud

Ice particles form in the low T near the top of the cloud

The ice particles fall and pull cold air down

The downdraft created, produces heavy rain or hail

EFFECTS OF THUNDERSTORMS

Flash Floods

Strong Winds

Hail

Heavy Rain

Lightning

TORNADO

• Most common are small and last only a few minutes

• May lift dust and debris from the ground

• Violently rotating column of air

• Stretches from a cloud to the ground

• Moves along the ground in a winding path

• Column may rise off the ground and then come down in a different place

EFFECTS OF TORNADOES

Most common can pick up and slam dirt and small objects

Large tornadoes can knock over large trees

20% can lift cars off the ground

Tear roofs off houses

1% can lift or completely demolish sturdy buildings

METEOROLOGIST

Scientist who studies weather

Uses maps to display a lot of information at once

To predict weather they look at past and current conditions

Use technology to gather information

Weather forecasters use advanced Technologies

Fronts

WEATHER DATA

Isobars: Lines that connect places with the same air pressure. Isotherms: Lines of equal temperature.

Pressure systems

H L

B G Y R

Precipitation

FORECASTING

I. Is complicated

II. Short forecasts are the most accurate (3 days)

III. Fast changing weather is less accurate (storms)

COMPUTERS IN WEATHER

A. Important tool for forecasting weather

B.Scientists study the computer forecasts then apply

their knowledge and experience

C.Combine many types of data to forecast what might

happen next

D.Can create maps when weather stations send in data

GATHERING WEATHER INFORMATION

Ground Stations

Gathers data from just one place

Small area surrounding the station

Satellites

Gathers data from a large area

Surface of Earth below