APPENDIX B:

GLOSSARY OF WEATHER TERMS

Thunderstorm Terms:

1. Cumulus Cloud - A cauliflower shaped cloud with a flat base and sharp edges. This cloud is a rising column of condensing air. As the cloud and cloud droplets grow in size, the base will begin to gray.

2. Towering Cumulus Cloud - A cumulus cloud that continues to grow so that its height is taller than or equal to its width. It is the first stage of growth into a thunderstorm. It may produce a shower.

3. Thunderstorm (Cumulonimbus) - A towering cumulus cloud that has continued to grow in height and width and now lightning is occurring. The storm may extend 5 to 10 miles high into the atmosphere and 5 to 25 miles across. Heavy rain and gusty winds often accompany the storm.

4. Precipitation Shaft - A visible column of rain or hail falling from the base of the cloud.

5. Hail - Precipitation in the form of balls or clumps of ice.

6. Squall Line - A solid line or band of active thunderstorms.

7. Anvil - An extension of the upper part of the thunderstorm created by strong winds within the upper portion of the atmosphere. It usually has a smooth appearance. With long lasting thunderstorms, the anvil may spread 100 miles downwind.

8. Mammatus (or Mamma Cloud) - This cloud appears to be hanging, with rounded protuberances or pouches on the underside of the cloud. With thunderstorms, this cloud is usually seen under the anvil. Mammatus is associated with severe thunderstorms.

9. Gust Front - The leading edge of the thunderstorm's downdraft of air as it spreads out away from the storm. It is associated with gusty cool winds and often precedes the thunderstorm's rain by several minutes.

10. Shelf Cloud - A low-level, wedge-shaped cloud attached to the thunderstorm. It forms above the gust front, as warm air ahead of the storm rides over the cool outflow from the thunderstorm.

11. Roll Cloud - On rare occasions, a shelf cloud may turn into a roll cloud. The motion of the warm air riding up and over the cool air moving down and under creates a swirling of air or an eddy. The cloud takes on the shape of a horizontal tube that appears to be rolling. It is detached from the thunderstorm on its leading edge.

12. Rain-Free Base - The dark underside of a cloud (its base) that has no visible precipitation falling from it. This marks the updraft of a thunderstorm.

13. Wall Cloud - This cloud appears as an abrupt lowering of the cloud base from the relatively flat rain-free base. It is attached to a thunderstorm and may be rotating. This is the portion of the thunderstorm from which the tornado often descends.

14. Funnel Cloud - A funnel-shaped cloud extending from a towering cumulus or thunderstorm. It is associated with a rotating column of air that has condensed to form a cloud.

15. Tornado - A violently rotating column of air in contact with the ground and extending to the thunderstorm base, often seen extending from near the wall cloud. It's size may range from a few yards across to a mile wide.

16. Flanking Line - A line of cumulus clouds connected to and extending outward from the most active portion of a parent cumulonimbus, usually found on the southwest (right, rear) side of a storm. The cloud line has roughly a stair step appearance with the taller clouds adjacent to the parent cumulonimbus. It is most frequently associated with strong or severe thunderstorms.

17. Hook Echo - A radar pattern sometimes observed in the southwest (right, rear) quadrant of a tornadic thunderstorm. The rain echo forms the hook pattern as air rotates around the strong updraft. The updraft is represented by the hollow portion of the hook (looks like a backwards "J" or a 6) and is where the tornado would most likely be found (if the storm were to produce one).

18. Scud Cloud - Fragmented low cloud often seen in association with and behind thunderstorm gust fronts. This cloud is ragged and wind torn and is not usually attached to the thunderstorm.

19. Updraft - An area of warm and moist rising air. As the air rises, it condenses into a visible cumulus or cumulonimbus cloud. The updraft fuels the storm. In an ordinary thunderstorm, air rises at 40 mph and in a severe thunderstorm, speeds may reach over 100 mph.

20. Downdraft - A column of cool air that sinks toward the ground. It is most often accompanied by rain.

21. Downburst - A sudden rush of cool air toward ground that can impact with speeds over 70 mph and produce damage similar to that of a tornado. It usually occurs near the leading edge of the storm and may occur in heavy rain.

22. Microburst - A small downburst effecting an area less than 2.5 km (approximately 1.5 mi) in diameter.

23. Macroburst - A downburst effecting an area greater than 2.5 km (approximately 1.5 mi) in diameter.

24. Severe Thunderstorm - A thunderstorm producing damaging winds or winds greater than 58 mph and/or hail three-quarters of an inch or greater in diameter.

Flood Terms:

1. Flash Flood - A flood that occurs suddenly during or shortly following heavy rain or from a sudden release of water as in a dam break. Small streams and creeks usually react the fastest to heavy rain and rise several feet in hours or even minutes.

2. River Flood - A flood on a large river such as the Ohio River which takes a tremendous amount of rain and usually develops over a period of one to two days. Rain water first runs into the small streams, which flow into the larger branches, which then flow into the main stem of the river.

4. Urban Flood - Flooding due to rapid runoff of rain off of pavement (rain can't soak into the ground so it runs downhill) and poor drainage areas, which can be deadly.

5. Bankfull - The maximum height of the river before it overflows its banks.

6. Flood Stage - The stage of the river at which property damage begins to occur. Flood stage often differs from bankfull. The river may overflow its banks into a flood plain without reaching flood stage.

7. Flood Crest - The highest stage that a river reaches during a flood event.




Winter Weather Terms:

1. Snow - A prediction of snow indicates a steady fall of snow for several hours or more. It may be modified by terms such as "light," "intermittent," or "occasional" to indicate lesser intensity or periodic snow.

2. Snow Flurries - Light snow falling for short durations, producing no accumulation to a dusting.

3. Snow Showers - Snow falling at varying intensities for brief time periods. Some accumulation is possible.

4. Snow Squalls - Brief, intense snow showers, accompanied by strong, gusty winds. Accumulations may be significant.

5. Drifting Snow - Falling snow or loose snow on the ground, being blown into mounds, causing uneven snow depths. The wind carries the snow near the ground, causing little or no restriction to visibility.

6. Blowing Snow - Wind-driven snow that causes reduced visibility and sometimes significant drifting. Blowing snow may be snow that is falling or snow that was once loose on the ground and has been picked up by the wind.

7. Heavy Snow - Snow accumulating 6 inches or more in 24 hours or less.

8. Lake Effect Snow - Snow, often heavy, produced by cold air moving across the warmer waters of the Great Lakes.

9. Blizzard - Sustained winds or frequent wind gusts of 35 mph or more, considerable snow or blowing snow (visibility less than 1/4 of a mile), and usually cold temperatures (generally below 20 F).

10. Sleet - Ice pellets or granules of frozen rain. Sleet occurs when rain falls into a layer of air with temperatures below freezing. Sleet usually bounces when hitting a surface and does not stick, but can accumulate on roadways, creating a hazard to motorists.

11. Freezing Rain - Rain that falls onto a surface with a temperature at or below freezing, causing it to freeze to the surface, forming a coating of ice or glaze.

12. Freezing Drizzle - Drizzle that falls onto a surface with a temperature at or below freezing, causing it to freeze to the surface, forming a thin coating of ice or rime. Drizzle is a very light precipitation with little accumulation, but even a small amount of ice can cause a problem.

13. Ice Storm - A significant and sometimes damaging accumulation of ice due to freezing rain. Significant ice accumulations are usually accumulations of 0.25 inches or greater.

14. Wind Chill (Wind chill factor) - Is based on the rate of heat loss from exposed skin, caused by the combined effects of wind and cold. As the wind increases, heat is carried away from the body at an accelerated rate, driving down the body temperature.

15. Freeze - Used when temperatures at or near the surface (ground) are expected to be 32 F or below. A freeze may or may not be accompanied by frost.

16. Frost - The formation of ice crystals in the forms of scales, needles, feathers, or fans, which develop under conditions similar to dew, except that the minimum temperature has dropped to 32 F or colder.

16. Hypothermia - When the body temperature drops below 95 F.

17. Frostbite - Damage to body tissue caused by that tissue being frozen.