Subj : Wx Terms (H)(1) To : All From : Daryl Stout Date : Sun Jul 09 2017 12:04 am H-Alpha In solar-terrestrial terms, this absorption line of neutral hydrogen falls in the red part of the visible spectrum and is convenient for solar observations. The H-alpha line is universally used for patrol observations of solar flares. H-component of the Geomagnetic Field (Geomagnetic Elements) In solar-terrestrial terms, the components of the geomagnetic field at the surface of the earth. In SESC use, the northward and eastward components are often called the H and D components, where the D component is expressed in gammas and is derived from D (the declination angle) using the small angle approximation. H0 On a buoy report, Significant Wave Height is the average height (meters) of the highest one-third of the waves during a 20 minute sampling period. H5 500 millibar level height (in a standard atmosphere this is near 5,500 meters (18,000 ft) H7 height of the 700 millibar level. In a standard atmosphere this is near 3,000 meters (10,000 ft) H8 height of the 850 millibar level. Hague Line The North Atlantic boundary between the U.S. and Canada fishing waters as determined by the World Court in The Hague, Netherlands. Hail Showery precipitation in the form of irregular pellets or balls of ice more than 5 mm in diameter, falling from a cumulonimbus cloud. Hail Contamination A limitation in NEXRAD rainfall estimates whereby abnormally high reflectivities associated with hail are converted to rainfall rates and rainfall accumulations. These high reflectivity values are mistaken by the radar for extremely heavy rain, thus "contaminating" (inflating) its estimation of how much rain has fallen over the affected area. Hail Index An indication of whether the thunderstorm structure of each storm identified is conducive to the production of hail. Hail Size Typically refers to the diameter of the hailstones. Warnings and reports may report hail size through comparisons with real-world objects that correspond to certain diameters: Description Diameter (inches) Pea 0.25 Marble or Mothball 0.50 Penny or Dime 0.75 Nickel 0.88 Quarter 1.00 Half Dollar 1.25 Walnut or Ping Pong Ball 1.50 Golfball 1.75 Hen's Egg 2.00 Tennis Ball 2.50 Baseball 2.75 Tea Cup 3.00 Grapefruit 4.00 Softball 4.50 Hail Spike An area of reflectivity extending away from the radar immediately behind a thunderstorm with extremely large hail. In an area of large hail, radiation from the radar can bounce from hailstone to hailstone before being reflected back to the radar. The time delay between the backscattered radiation from the storm and the bounced and scattered radiation from the large hail causes the reflectivity from the hail to appear to come from a farther range than the actual storm. Haines Index This is also called the Lower Atmosphere Stability Index. It is computed from the morning (12Z) soundings from RAOB stations across North America. The index is composed of a stability term and a moisture term. The stability term is derived from the temperature difference at two atmosphere levels. The moisture term is derived from the dew point depression at a single atmosphere level. This index has been shown to be correlated with large fire growth on initiating and existing fires where surface winds do not dominate fire behavior. The Haines Indices range from 2 to 6 for indicating potential for large fire growth. Halo Any of a variety of bright circles or arcs centered on the sun or moon, caused by the refraction or reflection of light by ice crystals suspended in the earth's atmosphere and exhibiting prismatic coloration ranging from red inside to blue outside. Hanging (ice) dam In hydrologic terms, a mass of ice composed mainly of frazil or broken ice deposited underneath an ice cover in a region of low flow velocity. Hazardous Weather Outlook A narrative statement produced by the National Weather Service, frequently issued on a routine basis, to provide information regarding the potential of significant weather expected during the next 1 to 5 days. 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. Haze (abbrev. HZ)- An aggregation in the atmosphere of very fine, widely dispersed, solid or liquid particles, or both, giving the air an opalescent appearance that subdues colors. HDD Heating Degree Days- A form of degree day used to estimate energy requirements for heating. Typically, heating degree days are calculated as how much colder the mean temperature at a location is than 65øF on a given day. For example, if a location experiences a mean temperature of 55øF on a certain day, there were 10 HDD (Heating Degree Days) that day because 65 - 55 = 10. HDRAIN An Hourly Digital Rainfall Product of the WSR-88D. Head In hydrologic terms, the difference between the pool height and tailwater height. Usually expressed in feet of head, or in lbs./sq. inch. Head Loss In hydrologic terms, the decrease in total head caused by friction. Head Race In hydrologic terms, a channel which directs water to a water wheel; a forebay. Headward Erosion In hydrologic terms, erosion which occurs in the upstream end of the valley of a stream, causing it to lengthen its course in such a direction. Headwater Basin In hydrologic terms, a basin at the headwaters of a river. All discharge of the river at this point is developed within the basin. Headwaters In hydrologic terms, streams at the source of a river. Heat Advisory Issued within 12 hours of the onset of the following conditions: heat index of at least 105øF but less than 115øF for less than 3 hours per day, or nighttime lows above 80øF for 2 consecutive days. Heat Exhaustion A mild form of heat stroke, characterized by faintness, dizziness, and heavy sweating. Heat Index The Heat Index (HI) or the "Apparent Temperature" is an accurate measure of how hot it really feels when the Relative Humidity (RH) is added to the actual air temperature. Heat Lightning Lightning that occurs at a distance such that thunder is no longer audible. Heat Stroke A condition resulting from excessive exposure to intense heat, characterized by high fever, collapse, and sometimes convulsions or coma. Without immediate medical attention, death may result. Heat Wave A period of abnormally and uncomfortably hot and unusually humid w eather. Typically a heat wave lasts two or more days. Heating Degree Days (abbrev. HDD) A form of degree day used to estimate energy requirements for heating. Typically, heating degree days are calculated as how much colder the mean temperature at a location is than 65øF on a given day. For example, if a location experiences a mean temperature of 55øF on a certain day, there were 10 HDD (Heating Degree Days) that day because 65 - 55 = 10. Heavy Freezing Spray An accumulation of freezing water droplets on a vessel at a rate of 2 cm per hour or greater caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement. Heavy Freezing Spray Warning A warning that may be issued within the Offshore Waters Forecast, the Coastal Waters Forecast, the Nearshore Marine Forecast, and the Open Lake Forecast (GLF). An accumulation of freezing water droplets on a vessel at a rate of 2 cm per hour or greater caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .