Weather A - Z (H-I)

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Weather A - Z (H-I)

Post by ICE » Fri Apr 28, 2006 9:45 am

Hail - A mixture of liquid and frozen precipitation. Hailstones are composed of layers of ice and can become quite large when strong gusts of upward-moving air keep them inside the cloud. As they move around inside the cloud they collide with raindrops, adding layers and growing before they fall to earth.

Hard Freeze - A freeze when the air temperature is 26 degrees or colder for at least four consecutive hours. It usually means that seasonal vegetation will be destroyed.

Haze - Tiny particles of dust, smoke, salt or pollution droplets that are scattered through the air. The particles are too small to be seen or felt individually, but they diminish visibility.

Heat Advisory - It’s issued within 12 hours of the onset of the following conditions: a heat index of at least 105 degrees but less than 115 degrees for less than 3 hours per day or if nighttime lows remain above 80 degrees for 2 consecutive days.

Heat Index - It’s the ‘feel like’ temperature on a hot day. The heat index is a number that expresses the warming effect of humidity at different temperatures. Only air temperature and relative humidity are used in the calculation of heat index.

Heat Lightning - There is no such thing as heat lightning. Heat lightning is just ordinary lightning, except that it is too far away for its thunder to be heard or the cloud producing it to be seen.

Heavy Snow Warning - It’s issued when a snowfall totaling 6 inches or more in 12 hours or less is expected. Also, it’s issued when there is 8 inches or more of snow in 24 hours or less.

High Pressure System - A whirling mass of cool, dry air that generally brings fair weather and light winds. When viewed from above, winds spiral out of a high-pressure center in a clockwise rotation in the Northern Hemisphere. These bring sunny skies.

High Wind Warning - It’s issued when winds of 40 mph or greater are occurring or expected to occur for at least one hour. It also occurs if winds of 58 mph or greater are expected.

High Wind Watch - It’s issued when conditions are favorable of the development of high winds.

Humidity - The amount of water vapor in the air.

Hurricane - They are intense storms with swirling winds up to 150 miles per hour. Usually around 300 miles across, hurricanes are 1,000-5,000 times larger than tornadoes. Hurricanes are known by different names around the world. In Japan they are Typhoons, while Australians call them Willy-Willys.

Hurricane Season - A six-month period from June 1 to Nov. 30, when conditions are favorable for hurricane development.

Hygrometer - An instrument that measures the water vapor content of air or the humidity.

Ice - A water substance in the solid phase.

Ice Storms - They occur when temperatures below a raining cloud are very cold, causing the raindrops to become supercooled (less than 32 degrees Fahrenheit). Freezing rain covers streets, houses, and trees with heavy layers of ice, causing concern for dangerous driving, and damage from the weight of the ice.

Ice Storm Warning - It’s issued when damaging accumulations of ice are expected during a freezing rain event.

Indian Summer - A warm, tranquil spell of weather in the autumn, especially after a period of cold weather. The term is used most often in the Midwest and New England.

Inversion - A layer in the atmosphere where the temperature increases with height.

Isobar - A line connecting equal points of pressure.

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