What’s Up With That Weather?

1. What’s Up With That Weather?

2. Why Does It Rain? • When rain clouds are pushed up into cold air the rain drops form and become heavy enough to be pulled to the ground by gravity. • Water from the sea, rivers, lakes, ponds, pools and puddles is heated by the sun and evaporated into water vapor. • Clouds are made up of millions of tiny water vapor droplets, which cling together.

3. What’s Snow? • Snow falls from clouds that contain enough cloud droplets and ice crystals for precipitation to form. • In order for snow to reach the ground without melting, the wet bulb temperature of the air near the ground must be below freezing. • The wet bulb temperature is the temperature measured by a thermometer that has a little wet sock covering the bulb before it is swung in a circle in the air. • Thus, you can have snow fall reaching the ground even when the air temperature is slightly above freezing.

4. Hurricanes • Hurricanes are severe tropical storms that form in the southern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern Pacific Ocean. • Hurricanes gather heat and energy through contact with warm ocean waters. Evaporation from the seawater increases their power. • Hurricanes rotate in a counter-clockwise direction around an "eye." • Hurricanes have winds at least 74 miles per hour. • When they come onto land, the heavy rain, strong winds and heavy waves can damage buildings, trees and cars. • The heavy waves are called a storm surge. • Storm surges are very dangerous and a major reason why you MUST stay away from the ocean during a hurricane warning or hurricane.

5. Lightning • The action of rising and descending air within a thunderstorm separates positive and negative charges. • Water and ice particles also affect the distribution of electrical charge. • Lightning results from the buildup and discharge of electrical energy between positively and negatively charged areas. • Most lightning occurs within the cloud or between the cloud and ground.

6. The Blowing Wind is moving air. The sun makes the wind blow. The energy in wind comes from the sun. When the sun shines it heats the earth. The air over the land gets hotter then the air over the water. The hot air raises and cooler air rushes in to take its place. The moving air is wind.

7. El Niño • In the tropical Pacific, trade winds generally drive the surface waters westward. • The surface water becomes warmer going westward because of its longer exposure to solar heating. • El Niño is observed when the easterly trade winds weaken, allowing warmer waters of the western Pacific to migrate eastward and eventually reach the South American Coast. • The cool nutrient-rich sea water normally found along the coast of Peru is replaced by warmer water depleted of nutrients, resulting in a dramatic reduction in marine fish and plant life.

8. References Suggested Reading • Why Does Lightning Strike? • Elmer's Weather • Sandra's Sun Hat Suggested Websites • The Water Cycle • Rain • The Weather Channel