1. Air masses and Air fronts
6th Grade Science: Weather

2. What influences Weather?
Weather is the short term state of the atmosphere
It depends on: temperature, humidity, precipitation, air pressure, wind and visibility
The water cycle is the movement of water between the atmosphere, the land, the oceans and living things
Evaporation water vapor in atmosphere
Condensation -----clouds
Precipitation -----rain/sleet/snow

3. Air Masses
An Air Mass is a large volume of air in which temperature and moisture content are nearly the same throughout.
It forms when the air over a region stays in one area for many days
Examples: hot and humid (#2) or cool and pleasant (#1)
Weather changes when an air mass moves into your area!

4. Air Fronts
A front forms between two air masses that meet; one air mass must run into another air mass
Density differences between the two masses causes mixing of the air and therefore weather activity
Warm = less dense
Cold = more dense
Occur in areas where there are big temperature differences-----such as the middle latitudes and not the equator.

5. Cold Front A cold front forms when cold air moves under warm air
A cold air mass is more dense and can push up a warmer air mass----it cools---clouds form
Storms that result are short but can bring heavy rain or snow
Cooler weather follows

6. Warm Front Warm fronts form when warm air moves over cold air
warm air masses can follow the retreat of a cold air mass
Warm air rises above the colder, denser air---cools, condenses and brings drizzling rain followed by warm clear weather

7. Stationary Front
Stationary fronts form when cold and warm air stop moving
Not enough wind for either air mass to advance
This can cause many days of unchanging weather, usually clear weather

8. Pressure Systems
Areas of different pressures can cause changes in weather
High pressure system = air sinks and warms
As the air sinks and spreads out, its gets warmer and turns liquid water into vapor so relative humidity decreases and clouds disappear
Clear skies and calm air or gentle breezes

9. Low pressure system= air rises and cools
Air converges and rises up---cools----forms clouds and rain/storms
Often can occur at fronts where there is a warm air mass converging with a cold air mass

10. A high air pressure system can form a low pressure system
Air moves out and away from high pressure centers to create the rising and cooling air at a low pressure center

11. Global Wind patterns Wind forms when there is unequal heating of
earths surface; which can cause air pressure
differences and therefore changes in
weather patterns all over the world
Globally, air moves from the poles
toward the equator
Wind brings air masses of different
temperatures and moisture contents to a region

12. wind belts
The Earth rotates so the air doesn’t move in a straight line, it curves!
Winds named by the direction they come from: We are in the Westerlies so which direction does our wind come from?

13. Jet Streams
Winds that travel high above the surface for a long period of time and at great speeds are Jet Streams!
Flow from West to East in a wavy pattern

14. Weather forecasting!
You now have just about all the ingredients it takes to be a weather forecaster! However, it takes professionals many more years of study to master the art!