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 65°F on a
given day. For example, if a location experiences a mean temperature of
55°F 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 105°F but less than 115°F for less than 3 hours
per day, or nighttime lows above 80°F 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 65°F on a given day.
For example, if a location experiences a mean temperature of 55°F 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 3.14-Win32
* Origin: The Thunderbolt BBS - Little Rock, Arkansas (618:250/33)