6.2 Meteorology. A meteorologist is a person who uses scientific principles to explain, understand, observe, or forecast Earth s weather.

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2 Water and Weather

3 6.2 Meteorology A meteorologist is a person who uses scientific principles to explain, understand, observe, or forecast Earth s weather.

4 6.2 Water in the Atmosphere Dew point is the temperature at which the rate of condensation is greater than the rate of evaporation. The higher the dew point the more humid the air feels.

5 When temperature increases, evaporation increases. When pressure increases, the rate of evaporation decreases. Condensation is a warming process because heat is released when water molecules change from a gas to a liquid.(this causes updrafts in a storm cell.) 6.2 Water in the atmosphere

6 6.2 Cloud formation Cumuliform clouds are formed as air masses rise because of convection. They appear piled up. Cumuliform clouds include: cirrocumulus altocumulus cumulus cumulonimbus

7 6.2 Cloud formation Stratiform clouds form when a large mass of stable air gradually rises, expands, and cools. They look like a blanket Stratiform clouds include: cirrostratus altostratus stratus nimbostratus

8 6.2 Cloud formation Clouds are a group of water droplets or ice crystals you can see in the atmosphere. Stratocumulus clouds are a cloud formation combining aspects of both cumuliform and stratiform clouds.

9 6.2 Cloud formation Cirrus clouds are thin lines of ice crystals high in the sky, above 6,000 meters. They are just a thin streak of white across a blue sky.

10 6.2 Rain Raindrops form when water vapor cools and condenses on a particle (dust, pollen, bacteria) in the troposphere. A raindrop will fall when it has enough mass for gravity to pull it down.

11 6.2 Frozen Precipitation Snow forms when water vapor condenses onto ice crystals in the troposphere. If snow passes through warmer air it will melt. If it refreezes before hitting the ground, it falls as sleet. If it doesn t freeze until hitting the ground, it falls as freezing rain.

12 6.2 Air masses and fronts The two main air masses that affect the U.S. are the Continental Polar and the Maritime Tropical. When any two air masses collide the border between them is called a front. Changing conditions and global winds cause these air masses to move.

13 6.2 Fronts A cold front occurs when cold air moves in and pushes warm air upward.

14 6.2 Fronts A warm front occurs when warm air moves in above existing cold air. A jet stream is found where there are sharp boundaries between cold and warm temperatures.

15 6.2 Fronts A cold front is shown on a weather map using a blue line marked with triangles facing the direction the front is moving. A warm front is shown using a red line marked with semicircles.

16 6.2 Low- and high-pressure areas A low-pressure center causes warm air to be pushed upward and cold air to rush in. The air flows counterclockwise around the center in the northern hemisphere. A high pressure center is where a stable cold air mass has settled in a region. It is associated with clear weather.

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18 6.2 Thunderstorms A warm air updraft and cooler air and rain downdraft form a storm cell in a cumulonimbus cloud. This is how thunderstorms form.

19 6.2 Storm Cells Hail forms when updrafts in a storm cell are strong enough to carry water droplets high in the troposphere where it s freezing. They grow when more water freezes onto them.

20 6.2 Lightning Lightning is a bright spark of light that occurs within a storm cloud, between a cloud and Earth s surface, or between two storm clouds.

21 A hurricane rotates counter-clockwise (NH) around a low-pressure center. Hurricanes form when the ocean is very warm, the air is very warm, and the wind conditions are just right. The usually occur in late summer/ early autumn. 6.2 Hurricanes

22 6.2 Tornadoes A tornado is a high speed vortex (whirling winds) around a lowpressure center. As the rotating wind pattern narrows and lengthens, it forms a funnel cloud.

23 6.2 El Nino Southern Oscillations Storm patterns across the globe can happen in cycles. Usually the trade winds blow warm water from east to west across the Pacific Ocean. Every so often the trade winds weaken and the warm water reverses direction.

24 6.2 El Nino Southern Oscillations Along with warm water comes greater thunderstorm activity across the Pacific. The change in wind flow, air pressure, and thunderstorm activity in the Pacific Ocean that causes decreased fish catches by Peruvian fisherman is known as El Niño.