- Slides: 54
Weather Patterns & Severe Storms Chapter 20
• small-area storms formed by the strong upward movement of warm, moist, unstable air • always accompanied by lightning, thunder, and usually rain • formed from cumulonimbus clouds
Observe an animation of a thunderstorm.
Air-mass thunderstorm: • form in warm, moist air mass • occur in spring and summer- last less than 1 hour • single, widely scattered
Frontal thunderstorm: • occur in lines along a frontal surface • stronger and may last several hours • can produce heavy rain and flooding
Lightning: • a discharge of electricity from a thundercloud to the ground, or cloud to cloud, or ground to cloud
• temperature inside lightning flash can reach 28, 000°C • at this temperature, air expands explosively-sudden expansion makes thunder!
an intense tropical lowpressure area with sustained winds starting at 75 mph
storm surge: currents formed when hurricanes pile water up along the shore and blow it inland most damaging part of a hurricane
eye: central area of sinking air; 15 to 20 km wide
Eye of hurricane Floyd
• Winds most violent just outside the eye
Check out this website! http: //www. weather. com/web/newscenter/specialreports/ hurricanes/inside/elements. html
Tropical depression: wind speeds up to 38 mph; some circular rotation at surface
Tropical storm: wind speeds from 39 -74 mph; can be named, shows drop in pressure, distinct rotation
Hurricane: wind speeds up to 75 mph
Movement of Air in a Hurricane
There are sometimes gaps in between these bands where no rain is found. In fact, if one were to travel between the outer edge of the hurricane to its center, one would normally progress from light rain to dry back to slightly more intense rain again over and over with each period of rainfall being more intense and lasting longer until reaching the eye. Upon exiting the eye and moving towards the edge of the hurricane, one would see the same events as they did going in, but in opposite order.
A schematic of this banding feature can be seen in the diagram above. The thunderstorms are now organized into regions of rising and sinking air. Most of the air is rising, but there is a small amount found in between the thunderstorms that is sinking.
a narrow, funnel-shaped column of spiral winds that extends downward from the cloud base and touches the ground
• strongest winds between 360 and 500 km/hr • funnel less than 500 m across • always travel with a parent thunderstorm at speeds ranging from 40 to 65 km/hr
funnel is a mixture of clouds and dust pressure gets lower in center lowering of condensation level due to low pressure causes cloud to funnel air flows toward the funnel and cools to dew point- drops form Extremely low pressure-when it touches ground, acts like a giant vacuum
Waterspout: tornados over the waterweaker than tornados
Tornados usually occur during spring and summer and most likely occur in late afternoon
Fujita Scale: scale used for categorizing tornados