• Weather Glossary (H)

    From Daryl Stout@57:57/10 to All on Wed Oct 28 00:05:56 2020
    This weather glossary contains information on more than 2000 terms,
    phrases and abbreviations used by the National Weather Service (NWS)...
    the government agency who makes weather forecasts, and issues weather advisories, watches, and warnings, for the United States, and its
    territories.

    Many of these terms and abbreviations are used by NWS forecasters to communicate between each other and have been in use for many years and
    before many NWS products were directly available to the public. It is the purpose of this glossary to aid you in better understanding NWS products.

    ***

    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 65F on a
    given day. For example, if a location experiences a mean temperature of
    55F 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 105F but less than 115F for less than 3 hours
    per day, or nighttime lows above 80F 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 65F on a given day.
    For example, if a location experiences a mean temperature of 55F 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.

    Heavy Snow
    This generally means...

    Snowfall accumulating to 4" or more in depth in 12 hours or less; or
    Snowfall accumulating to 6" or more in depth in 24 hours or less

    In forecasts, snowfall amounts are expressed as a range of values,
    e.g., "8 to 12 inches." However, in heavy snow situations where there is considerable uncertainty concerning the range of values, more appropriate phrases are used, such as "...up to 12 inches..." or alternatively
    "...8 inches or more...".

    Heavy Snow Warning
    Issued by the National Weather Service when snowfall of 6 inches (15 cm)
    or more in 12 hours or 8 inches (20 cm) or more in 24 hours is imminent
    or occurring. These criteria are specific for the Midwest and may vary regionally.

    Heavy Surf Advisory
    An advisory issued by the National Weather Service for fast moving deep
    water waves which can result in big breaking waves in shallow water
    (the surf zone).

    Hectopascal
    A unit of pressure equal to a millibar (1 hPa = 1 mb). Abbreviated hPa.

    Height
    In meteorology, usually a reference to Geopotential Height; roughly the
    height above sea level of a pressure level. For example, if a station
    reports that the 500 mb height at its location is 5600 m, it means that
    the level of the atmosphere over that station at which the atmospheric
    pressure is 500 mb is 5600 meters above sea level. This is an estimated
    height based on temperature and pressure data.

    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.

    Hertz
    (abbrev. Hz)- An international unit of frequency equal to one cycle per
    second, and named after a German physicist.

    HI
    High- In meteorology, a region of high pressure; also known as anticyclone.

    HIC
    Hydrologist In Charge

    High
    (abbrev. HI)- In meteorology, a region of high pressure; also known as anticyclone.

    High Clouds
    These clouds have bases between 16,500 and 45,000 feet in the mid
    latitudes. At this level they are composed of primarily of ice crystals.
    Some clouds at this level are cirrus, cirrocumulus, and cirrostratus.

    High Energy Event
    In solar-terrestrial terms, flares (class two or more) with outstanding Centimetric Bursts and SID. High Energy Protons are reported at the
    Earth in case of most of these events occurring on the western part of
    solar disk. (Class X flares).

    High Frequency (HF)
    The portion of the radio frequency spectrum between between 3 and 30 MHz.

    High Latitudes
    With specific reference to zones of geomagnetic activity, "high
    latitudes" refers to 50 to 80 geomagnetic.

    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, including
    strong to violent tornadoes, among other forms of severe weather.

    High Seas Forecast
    (HSF) - Marine forecasts for the major oceans of the world. In this
    context, major gulfs or seas (e.g., the Gulf of Mexico or the Bering Sea)
    are included within these forecast areas. Areas of responsibility for
    the U.S. are determined by international agreements under the auspices
    of the World Meteorological Organization (WMO).

    High Surf
    Large waves breaking on or near the shore resulting from swells spawned
    by a distant storm.

    High Surf Advisory
    A High Surf Advisory is issued when breaking wave action poses a threat
    to life and property within the surf zone. High surf criteria vary by
    region. High Surf Advisories are issued using the Coastal and Lakeshore
    Hazard Message (CFW) product.

    High Surf Warning
    A High Surf Warning is issued when breaking wave action results in an especially heightened threat to life and property within the surf zone.
    High surf criteria vary by region. High Surf Warnings are issued using
    the Coastal and Lakeshore Hazard Message (CFW) product.

    High Wind
    Sustained wind speeds of 40 mph or greater lasting for 1 hour or longer,
    or winds of 58 mph or greater for any duration.

    High Wind Advisory
    This product is issued by the National Weather Service when high wind
    speeds may pose a hazard. The criteria for this advisory varies from
    state to state. In Michigan, the criteria is sustained non-convective
    (not related to thunderstorms) winds greater than or equal to 30 mph
    lasting for one hour or longer, or winds greater than or equal to 45
    mph for any duration.

    High Wind Warning
    This product is issued by the National Weather Service when high wind
    speeds may pose a hazard or is life threatening. The criteria for this
    warning varies from state to state. In Michigan, the criteria is
    sustained non-convective (not related to thunderstorms) winds greater
    than or equal to 40 mph lasting for one hour or longer, or winds
    greater than or equal to 58 mph for any duration.

    High Wind Watch
    This product is issued by the National Weather Service when there is
    the potential of high wind speeds developing that may pose a hazard or
    is life threatening. The criteria for this watch varies from state to
    state. In Michigan, the criteria is the potential for sustained
    non-convective (not related to thunderstorms) winds greater than or
    equal to 40 mph and/or gusts greater than or equal to 58 mph.

    High-Speed Stream
    In solar-terrestrial terms, a feature of the solar wind having velocities
    that are about double average solar wind values.

    Hinge Crack
    In hydrologic terms, a crack caused by significant changes in water level.

    HLS
    Hurricane Local Statement

    HMD
    (Hemispheric Map Discussion)- This discussion is issued once a day around
    1 PM EST (2 PM EDT) and is primarily intended to provide insight into the hemispheric circulation patterns over the next 5 days. This includes a discussion of the 5-day mean circulation pattern. Comparisons,
    differences, and continuity among the numerical models are highlighted,
    and preferred solutions are proposed with an explanation of why a
    solution is preferred. This includes any reasons why the preferred
    solution differs from any model. In cases where certain models are not universally available, an attempt will be made to describe that model's solution to an extent that a reader can understand it's important aspects.

    HND
    Hundred

    Hoar Frost
    A deposit of interlocking crystals formed by direct sublimation on
    objects, usually those of small diameter freely exposed to the air, such
    as tree branches, plants, wires, poles, etc. The deposition of hoar frost
    is similar to the process by which dew is formed, except that the
    temperature of the frosted object must be below freezing. It forms when
    air with a dew point below freezing is brought to saturation by cooling.

    Hodograph
    A polar coordinate graph which shows the vertical wind profile of the
    lowest 7000 meters of the atmosphere. These plots are used to determine
    the advection patterns aloft, whether a thunderstorm will rotate, and
    the type of thunderstorms that you will likely see that day.

    Homologous Flares
    In solar-terrestrial terms, solar flares that occur repetitively in the
    same active region, with essentially the same position and with a common pattern of development.

    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.

    Horizon
    The distant line along with the earth and sky appear to meet.
    Obstructions are not considered as part of the horizon.

    Hourly Precipitation Data (HPD)
    It contains data on nearly 3,000 hourly precipitation stations
    (National Weather Service, Federal Aviation Administration, and
    cooperative observer stations) in inches to tenths or inches to
    hundredths at local standard time. HPD includes maximum precipitation
    for nine (9) time periods from 15 minutes to 24 hours, for selected
    stations.

    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.

    hPa
    Hectopascal- A unit of pressure equal to a millibar (1 hPa = 1 mb).

    HPC
    Hydrometeorological Prediction Center

    HR
    Hour

    HRS
    hours

    HSA (Hydrologic Service Area)
    A geographical area assigned to Weather Service Forecast
    Office's/Weather Forecast Office's that embraces one or more rivers.

    Humidity
    Generally, a measure of the water vapor content of the air. Popularly,
    it is used synonymously with relative humidity.

    Humidity Recovery
    The change in relative humidity over a given period of time; generally
    between late evening and sunrise. The moisture change in the fine fuels
    during this period is directly related to the amount of humidity
    recovery.

    Hummock
    In hydrologic terms, a hillock of broken ice which has been forced
    upward by pressure.

    Hummocked Ice
    In hydrologic terms, ice piled haphazardly one piece over another to
    form an uneven surface.

    Hurricane
    (abbrev. HURCN) A tropical cyclone in the Atlantic, Caribbean Sea,
    Gulf of Mexico, or eastern Pacific, which the maximum 1-minute sustained surface wind is 64 knots (74 mph) or greater.

    Hurricane Force Wind Warning
    A warning for sustained winds, or frequent gusts, of 64 knots (74 mph)
    or greater, either predicted or occurring, and not directly associated
    with a tropical cyclone.

    Hurricane Local Statement
    A public release prepared by local National Weather Service offices in
    or near a threatened area giving specific details for its county/parish
    warning area on

    (1) weather conditions
    (2) evacuation decisions made by local officials
    (3) other precautions necessary to protect life and property.

    Hurricane Season
    The part of the year having a relatively high incidence of tropical
    cyclones. In the Atlantic, Caribbean, and Gulf of Mexico, and central
    North Pacific, the hurricane season is the period from June through
    November; in the eastern Pacific, May 15 through November 30. Tropical
    cyclones can occur year-round in any basin.

    Hurricane Warning
    A warning that sustained winds 64 kt (74 mph or 119 kph) or higher
    associated with a hurricane are expected in a specified coastal area
    in 24 hours or less. A hurricane warning can remain in effect when
    dangerously high water or a combination of dangerously high water and exceptionally high waves continue, even though winds may be less than
    hurricane force.

    Hurricane Watch
    An announcement of specific coastal areas that a hurricane or an
    incipient hurricane condition poses a possible threat, generally
    within 36 hours.

    HV
    have

    HVY
    Heavy

    HWVR
    However

    Hyder Flare
    In solar-terrestrial terms, a filiment-associated two-ribbon flare,
    often occurring in spotless regions. The flare presumably results from
    the impact on the chromosphere of infalling filament material.

    Hydraulic Fill Dam
    In hydrologic terms, a dam constructed of materials, often dredged, that
    are conveyed and placed by suspension in flowing water.

    Hydraulic Flow
    Atmospheric flow that is similar in character to the flow of water over
    an obstacle.

    Hydraulic Grade Line
    In hydrologic terms, a line whose plotted ordinate position represents
    the sum of pressure head plus elevation head for the various positions
    along a given fluid flow path, such as along a pipeline or a ground
    water streamline.

    Hydraulic Head
    In hydrologic terms,

    (1) The height of the free surface of a body of water above a given
    point beneath the surface.

    (2) The height of the water level at the headworks, or an upstream point,
    of a waterway, and the water surface at a given point downstream.

    (3) The height of a hydraulic grade line above the center line of a
    pressure pipe, at a given point.

    Hydraulic Jump
    A steady disturbance in the lee of a mountain, where the airflow passing
    over the mountain suddenly changes from a region of low depth and high
    velocity to a region of high depth and low velocity.

    Hydraulic Permeability
    In hydrologic terms, the flow of water through a unit cross-sectional
    area of soil normal to the direction of flow when the hydraulic gradient
    is unity.

    Hydrograph
    In hydrologic terms, a graph showing the water level (stage), discharge,
    or other property of a river volume with respect to time.

    Hydrograph Separation
    In hydrologic terms, the process where the storm hydrograph is separated
    into baseflow components and surface runoff components.

    Hydrographic Survey
    In hydrologic terms, an instrumental survey to measure and determine characteristics of streams and other bodies of water within an area,
    including such things as location, areal extent, and depth of water in
    lakes or the ocean; the width, depth, and course of streams; position
    and elevation of high water marks; location and depth of wells, etc.

    Hydrologic Budget
    In hydrologic terms, an accounting of the inflow to, outflow from, and
    storage in, a hydrologic unit, such as a drainage basin, aquifer, soil
    zone, lake, reservoir, or irrigation project.

    Hydrologic Cycle
    The description of the transport of water substance between the earth,
    the atmosphere, and the seas.
    or
    In hydrologic terms, the natural pathway water follows as it changes
    between liquid, solid, and gaseous states.

    Hydrologic Equation
    In hydrologic terms, the water inventory equation (Inflow = Outflow +
    Change in Storage) which expresses the basic principle that during a
    given time interval the total inflow to an area must equal the total
    outflow plus the net change in storage.

    Hydrologic Model
    In hydrologic terms, a conceptual or physically-based procedure for
    numerically simulating a process or processes which occur in a watershed.

    Hydrologic Service Area
    HSA. A geographical area assigned to Weather Service Forecast
    Office's/Weather Forecast Office's that embraces one or more rivers.

    Hydrology
    The scientific study of the waters of the earth, especially with
    relation to the effects of precipitation and evaporation upon the
    occurrence and character of water on or below the land surface.

    Hydrometeor
    A particle of condensed water (liquid, snow, ice, graupel, hail) in the atmosphere.

    Hydrometeorologists
    In hydrologic terms, individuals who have the combined knowledge in the
    fields of both meteorology and hydrology which enables them to study and
    solve hydrologic problems where meteorology is a factor.

    Hydrometeorology
    The part of meteorology that pertains to hydrology.

    Hydrostatic Head
    In hydrologic terms, a measure of pressure at a given point in a liquid
    in terms of the vertical height of a column of the same liquid which
    would produce the same pressure.

    Hydrometeorology
    An interdisciplinary science involving the study and analysis of the interrelationships between the atmospheric and land phases of water as
    it moves through the hydrologic cycle.

    Hyetograph
    A graphical representation of rainfall intensity with respect to time.

    Hygrometer
    An instrument which measures the humidity of the air.

    Hygroscopic
    Absorbing or attracting moisture from the air.

    Hypothermia
    A rapid, progressive mental and physical collapse that accompanies the
    lowering of body temperature.

    HZ
    1) Haze- 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.

    (or)

    2) Hertz- An international unit of frequency equal to one cycle per
    second, and named after a German physicist.
    --- SBBSecho 3.11-Win32
    * Origin: The Thunderbolt BBS - tbolt.synchro.net (57:57/10)