1. WEATHER What is it?

2. To Review:

4. Fronts Fronts are the line boundary lines where two chunks (masses) of cold and warm air meet. Storms often occur at fronts. Cold Front - cold air replaces warm air (shown by a blue line with triangles pointing to where the air is moving) The warm air, which hold a lot of water vapor, gets pushed upward quickly When a cold front passes through, temperatres can drop more than 15 degrees within the first hour – usually causes heavy rain, sometimes with hail, thunder and lightening. This type of storm is often violent, but it ends quickly

6. Warm Fronts Warm air replaces cold air – shown by sold red line with semicircles pointing toward the colder air and in the direction of movement Warm, humid air eventually rises high enough for water droplets and clouds to form, and rain to fall When warm front passes through, the air becomes noticeably warmer and more humid than before. Precipitation will be steady rain and will last longer than a cold front.

7. Warm Front

8. Other Fronts Stationary Front - a pair of air masses, neither of which is strong enough to replace the other. On a weather map, this is shown by an inter-playing series of blue spikes pointing one direction and red domes pointing the other. Always stay still. The weather is clear to partly cloudy. If both of the air masses are relatively dry, then no precipitation will fall. However, in some stationary fronts where there is a lot of water vapor in the warmer air mass, significant rain or freezing rain can occur. Occluded Front A composite front formed when a cold front overtakes a warm front and forces it aloft. Usually form around areas of low atmospheric pressure. There is often precipitation along an occluded front from cumulonimbus or nimbostratus clouds. Wind changes direction as the front passes and the temperature changes too.

9. Clouds Cirrus Clouds – high clouds, clear skies, warm temperatures, no precipitation, formed from ice crystals, called thin, wispy or stringy

10. Cumulus Clouds – Middle clouds. The clouds you learned to draw at an early age and that serve as the symbol of all clouds. Their tops are rounded, puffy, and a brilliant white when sunlit, while their bottoms are flat and relatively dark. Develop on clear, sunny days when the sun heats the ground directly below. Possible precipitation 10-50%

11. Stratus Clouds – Low clouds, looks like a flat blanket, arranged in layers, cloudy skies, usually gray in color, cool temperatures, good chance for precipitation (50% or higher)

12. Cumulonimbus Clouds – Storm clouds that form in all layers of the atmosphere, strong winds, heavy precipitation, dark in color. Nimb = rain producing

13. Jet Streams The atmosphere has currents just like the ocean – these are called jet streams Jet streams are strong, high speed air currents that occur far above the atmosphere They circle the globe Reach highest speeds during winter months

14. Polar Jet Stream – have strongest, highest speeds during winter Occur west to east around the North and South Poles Subtropical Jet Stream – occurs West to East and just south of the equator Equatorial jet stream – occurs East to West slightly above the equator

15. Weather Instruments Tools that meteorologists use To measure and predict weather

16. Hygrometer - measures the humidity or moisture in the air (the amount of water vapor)

17. Thermometer - measures air temperature

18. Anemometer – measures wind speed

19. Rain Gauge – measures the amount of rain that has fallen over a specific time period

20. Weather Vane – determines the direction the wind is blowing.

21. Doppler Radar – a radar tracking system that determines the location and velocity of a storm, clouds or precipitation

22. Weather balloon – a balloon that is sent into the atmosphere to take measurements of air pressure, temperature, etc in the layers of the atmosphere.

23. WINDS

24. Which way is the wind blowing? Named for the direction from which the wind is blowing If the wind is blowing from the southwest (SW), the the winds are considered SW N, W, E, S, NW, SW, NE, SE

25. Wind is caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds

26. LAND AND SEA BREEZES Unequal heating of air over land and water results in breezes near shorelines. While the land is warm during the day, air above it rises, and a cool breeze blows in from the sea. As the land cools off at night, air pressure over it increases, and a cool land breeze blows out to the sea.

27. MOUNTAIN AND VALLEY BREEZES Valley Breeze – during the day, the sun heats up valley air rapidly. This causes it to rise, causing a warm, up-slope wind.

28. Mountain Breeze – At night, the process is reversed. Mountain air cools rapidly at night and “falls” down slope, causing a wind going in the other direction.

29. RAIN SHADOWS A rain shadow is a patch of land that has been forced to become a desert because mountain ranges blocked all plant-growing, rainy weather. On one side of the mountain, wet weather systems drop rain and snow. On the other side of the mountain—the rain shadow side—all that precipitation is blocked. In a rain shadow, it’s warm and dry. On the other side of the mountain, it’s wet and cool. Why is there a difference? When an air mass moves from a low elevation to a high elevation, it expands and cools. This cool air cannot hold moisture as well as warm air. Cool air forms clouds, which drop rain and snow, as it rises up a mountain. After the air mass crosses over the peak of the mountain and starts down the other side, the air warms up and the clouds dissipate. That means there is less rainfall.