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 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.
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