29 results. (Showing 1 - 20)

1. hail
Precipitation in the form of circular or irregular-shaped lumps of ice.

2. halos
Rings or arcs that seem to encircle the sun or moon. They are caused by the refraction of light through the ice crystals in cirrus clouds.

3. Hazards Assessment
CPC's Hazards Assessment provides emergency managers, planners, forecasters and the public advance notice of potential hazards related to climate, weather and hydrological events.

4. haze
Fine dry or wet dust or salt particles in the air that reduce visibility.

5. health advisory
Issued by the Jefferson County Kentucky Air Pollution District when ground level ozone readings are expected to reach the moderate level. Persons with heart or respiratory problems should reduce physical exertion and outdoor activity.

6. health bulletin
Issued by the Jefferson County Kentucky Air Pollution District when ground level ozone readings are expected to reach the upper-moderate level. Elderly and persons with heart or respiratory problems should stay indoors and reduce physical activity. Motorists are asked to reduce unnecessary driving by using car pools or public transportation.

7. health warning
Issued by the Jefferson County Kentucky Air Pollution District when ground level ozone readings are expected to be in the unhealthful range. Elderly and persons with heart or respiratory problems should stay indoors near a fan or circulating air if possible, and reduce physical activity. Motorists are asked to reduce unnecessary driving by using car pools or public transportation.

8. heat advisory
Issued for expected daytime heat indices above 105F and nighttime heat indices above 80F for two or more consecutive days.

9. heat index
Heat kills by taxing the human body beyond its abilities. In a normal year, about 175 Americans succumb to the demands of summer heat. Human bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and as a last resort, by panting, when blood is heated above 98.6°F. Sweating, by itself, does nothing to cool the body, unless the water is removed by evaporation. High relative humidity retards evaporation. Heat disorders generally have to do with a reduction or collapse of the body's ability to shed heat by circulatory changes and sweating. When heat gain exceeds the level the body can remove, the temperature of the body's inner core begins to rise and heat related illnesses may develop.

10. Heating Degree Days
A form of degree-day used to estimate energy requirements for heating.

11. heavy snow warning
Issued for expected snowfall amounts of 4 inches or more in 12 hours or 6 inches or more in 24 hours. Snow is the only precipitation type expected.

12. heavy surf advisory
Advises people that heavy (high) surf may pose a threat to life or property. Such advisories may be issued alone or in conjunction with coastal flood watches or warnings.

13. HectoPascals (hPa )
1 hPA= 1 millibar, a unit of pressure.

14. Helicity
A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve. Helicity is proportional to the strength of the flow, the amount of vertical wind shear, and the amount of turning in the flow (i.e. vorticity). Atmospheric helicity is computed from the vertical wind profile in the lower part of the atmosphere (usually from the surface up to 3 km), and is measured relative to storm motion. Higher values of helicity (generally, around 150 m2/s2 or more) favor the development of mid-level rotation (i.e. mesocyclones). Extreme values can exceed 600 m2/s2.

15. high
The center of an area of high pressure, accompanied by anticyclonic and outward wind flow in the northern hemisphere. Also known as an anticyclone.

16. High Risk (of severe thunderstorms)
Severe weather is expected to affect more than 10 percent of the area. A high risk is rare, and implies an unusually dangerous situation and usually the possibility of a major severe weather outbreak.

17. high wind warning
Used when sustained winds of 40 mph or greater are expected to last for 1 hour or longer, or for non-thunderstorm winds of 58 mph or greater for any duration.

18. Hodograph
A plot representing the vertical distribution of horizontal winds, using polar coordinates. A hodograph is obtained by plotting the end points of the wind vectors at various altitudes, and connecting these points in order of increasing height. Interpretation of a hodograph can help in forecasting the subsequent evolution of thunderstorms (e.g., squall line vs. supercells, splitting vs. non-splitting storms, tornadic vs. nontornadic storms, etc.).

19. Hook (or Hook Echo)
A radar reflectivity pattern characterized by a hook-shaped extension of a thunderstorm echo, usually in the right-rear part of the storm (relative to its direction of motion). A hook often is associated with a mesocyclone, and indicates favorable conditions for tornado development.

20. HP Storm or HP Supercell
High-Precipitation storm (or High-Precipitation supercell). A supercell thunderstorm in which heavy precipitation (often including hail) falls on the trailing side of the mesocyclone. Precipitation often totally envelops the region of rotation, making visual identification of any embedded tornadoes difficult and very dangerous. Unlike most classic supercells, the region of rotation in many HP storms develops in the front-flank region of the storm (i.e., usually in the eastern portion). HP storms often produce extreme and prolonged downburst events, serious flash flooding, and very large damaging hail events. Mobile storm spotters are strongly advised to maintain a safe distance from any storm that has been identified as an HP storm; close observations (e.g., core punching) can be extremely dangerous.