Weather Fronts

1. Weather Fronts Part 2 Mrs. Nagrone

2. Objectives • You will have the understanding of how air masses and the collision of air masses cause weather conditions. • You will also be able to identify which air masses, global wind belts, and types of fronts usually control weather in the US.

3. Air Masses • Air pressure is the weight of air pressing down on an area. • A change in air pressure usually means a change in weather. • When a new system arrives it will have a different amount of air pressure.

4. Wind Belts • Polar Easterlies:Cold wind from the east. • Prevailing Westerlies: Blowing from west to east. • Northeast Trade Winds: Winds from Europe to N. America. • Southeast Trade Winds: Blow from SE to NW. • Prevailing Westerlies:Cause the weather in Africa and S. America. • Polar Easterlies:Move polar air toward the equator to keep temp. in balance.

5. Fronts • The border between two air masses that collide is called a front. • The masses usually do not mix but rather the faster pushes out the slower. • The warmer air will always be pushed up over the denser, cooler air. • There are four types of fronts.

6. Warm Front • When a warm mass moves into an area of cooler air the boundary that forms is called a warm front. • Warm air rises and cool air is lower. • High cirrus clouds usually precede a warm front. • They are followed by lower clouds causing precipitation.

7. Cold Front • The leading edge of a cold air mass causes a cold front as it collides with warm air. • Cold fronts travel quicker than warm and are more extreme. • The cold dense air pushes under the warm moist air causing condensing. • Usually heavy precipitation is evident.

8. Stationary Fronts • When the boundary between two fronts does not move it is called a stationary front. • Air masses mix and clouds form on both sides of the front. • When a warm front or cold front stalls it is called a stationary front.

9. Occluded Front • This front is what happens when a cold front overtakes a warm front. • The cold mass pushes all the way under the warm mass until it reaches the cold mass ahead of the warm mass. • The warm mass is trapped above the cooler air. • Precipitation flows light and steady in this front.

10. Water Cycle and Weather • The heat from the sun generates the energy needed for the water cycle. • Heat is needed for evaporation and condensation to occur. • Water from oceans, lakes and rivers provides what we need for precipitation to “recycle”.

11. Summary • Air masses that pass over an area control its weather. • A front is where two air masses collide. • Warm fronts bring steady rain and cloudy skies. • Cold fronts move quickly with strong storms. • Fronts that stay in place are called stationary fronts. • When a cold front overtakes a warm front an occluded front forms. • The water cycle provides the moisture needed to form clouds and precipitation.