1. Forecasting Weather

2. What are Fronts?
A boundary between two air masses is called a __Front_________
The shape of the _Front_______ depends on the density of the air masses and their speed

3. When a front forms:
Pressure falls when a front approaches (low pressure edges of air masses move in)
Changes in wind direction occur. High pressure air moves Clockwise, low pressure air moves Counterclockwise
Temperature changes occur
Precipitation occurs and can be in the form of strong storms

4. Low pressure is associated with the formation of clouds and precipitation.
Warm air rises and when it reaches a certain elevation it cools and become saturated.
Clouds form and when they are saturated, it precipitates

5. There are four main types of fronts

6. Warm Front:
Warmer air invades a cold air mass and is lifted over and replaces cooler air.
Cirrus and stratus clouds are associated with warm fronts
Gentle rain for days, slow clearing, and rising temperatures follow

7. Cold Front
Cooler air invades a warm air mass and moves under the warm air and replaces it
Cumulus clouds and thunderstorms produce HEAVY RAIN for a short period of time
Cooler temperatures and
clear and fair weather invade the area once the storms have passed

8. Stationary Front
Occurs when pressure differences cause a warm front or cold front to stop moving
It may remain in the SAME area for a few days.
Weather conditions include light winds and precipitation across the entire frontal region.

9. Occluded Front
Results from two cool air masses merging and forcing warmer air between them to rise
Strong winds and heavy precipitation may occur

10. How do weather systems move?
Weather systems move across North America from West to East.

11. Weather forecasting
Making predictions about future weather based on weather data.

12. Weather Maps Provide data from stations all over the earth
Help meteorologists forecast weather
Data included:
Temperature, air pressure, change in air pressure during the last three hours, wind speed, direction, dew point, visibility, cloud cover, cloud types and precipitation.

14. Isobars
Isobars - pressure lines drawn on weather maps to connect places having equal air pressure.
Isobars that are close together indicate a large pressure difference over a small area

15. Isotherms
Isotherms are lines drawn to connect places having equal temperatures

16. High and Low Pressure
Pressure is indicated in the middle of the isobars
H stands for a high pressure center
L stands for a low pressure center.
Winds develop and move from high to low pressure areas.

18. Technology and Weather Forecasting
Satellites photograph sections of the earth’s surface and show cloud coverage

19. Air Mass
A large body of air that has the same properties as the surface over which it develops
An air mass over the GULF of MEXICO would be warm and moist
An air mass over CANADA would be cool and dry

20. Air masses Cool and dry --> high pressure, low humidity CANADA
Warm and moist --> low pressure, high humidity GULF of MEXICO

21. Thunderstorms Occur inside warm moist air masses and fronts
Result when warm moist air rises quickly and cools and condenses rapidly
Heavy raindrops fall, dragging air with them, creating strong winds
Produced by cumulonimbus clouds

22. Lightning
Atoms of air which are caught in the strong winds lose and gain electrons, creating cloud regions which are positively or negatively charged
Currents flow between these regions resulting in lightning

23. Thunder
Rapid heating and cooling of air due to lightning (rapid expanding and contracting)

24. Tornado Forms along fronts
Wind at different heights blows in different directions and at different speeds
This along with a strong updraft produces a rotation

25. Hurricanes
A low pressure area develops where the ocean water is very warm
Trade winds blowing in opposite directions meet causing a swirl of air that is rotating
As moist air rises over the low pressure system, it cools and condenses and begins to descend
This pattern is repeated over and over

26. Clouds - condensed water vapor
Recipe for a Cloud:
Water vapor
Condensation nuclei (dust, smoke, ice, salt)
Relative humidity of 100% - saturation point or dew point

27. Types of Clouds: Stratus
fair weather or precipitation
Layers of sheets of clouds, can be dull gray blanket of clouds
Low altitude clouds
See pages

28. Types of Clouds: Cumulus
White puffy clouds with flat bases
Formed when moist air rises
Fair weather or thunderstorms
See pages

29. Types of Clouds: Cirrus
Wispy
High altitude
Contain ice crystals
Fair weather
See pages