A temperature scale where water at sea level has
a freezing point of +32 degrees F (Fahrenheit)
and a boiling point of +212 degrees F. More
commonly used in areas that observe the English
system of measurement. Created in 1714 by
Gabriel Daniel Fahrenheit (1696-1736), a German
physicist, who also invented the alcohol and
On the Beaufort Wind Scale, a wind with speeds
from 28 to 55 knots (32 to 63 miles per hour).
For marine interests, it can be categorized as a
moderate gale (28 to 33 knots), a fresh gale (34
to 40 knots), a strong gale (41 to 47 knots), or
a whole gale (48 to 55 knots). In 1964, the
World Meteorological Organization defined the
categories as near gale (28 to 33 knots), gale
(34 to 40 knots), strong gale (41 to 47 knots),
and storm (48 to 55 knots).
The amount of water vapor in the air. It is
often confused with relative humidity or dew
point. Types of humidity include absolute
humidity, relative humidity, and specific
An instrument that measures the water vapor
content of the atmosphere. See the psychrometer
as an example.
A nautical unit of speed equal to the velocity
at which one nautical mile is traveled in one
hour. Used primarily by marine interests and in
weather observations. A knot is equivalent to
1.151 statute miles per hour or 1.852 kilometers
Refers to the water vapor content in the
atmosphere, or the total water, liquid, solid or
vapor, in a given volume of air.
A wind that blows from one direction more
frequently than any other during a given period,
such as a day, month, season, or year.
An instrument used to measure water vapor
content of the atmosphere. It consists of two
thermometers, a wet bulb and dry bulb. May also
be referred to as a sling psychrometer.
A type of humidity that considers the ratio of
the actual vapor pressure of the air to the
saturation vapor pressure. It is usually
expressed in percentage.
To treat or charge something to the point where
no more can be absorbed, dissolved, or retained.
In meteorology, it is used when discussing the
amount of water vapor in a volume of air.
The point when the water vapor in the atmosphere
is at its maximum level for the existing
A diurnal coastal breeze that blows onshore,
from the sea to the land. It is caused by the
temperature difference when the surface of the
land is warmer than the adjacent body of water.
Predominate during the day; it reaches its
maximum early to mid afternoon. It blows in the
opposite direction of a land breeze.
Dependent on the temperature and the humidity of
the air, it is the difference between the dry
bulb and the wet bulb readings.
A thermometer used to measure the lowest
temperature in the ambient atmosphere in its
natural state by evaporating water from a wet
muslin-covered bulb of a thermometer. The wet
bulb temperature is used to compute dew point
and relative humidity. One of the two
thermometers that make up a psychrometer.
Air that flows in relation to the earth's
surface, generally horizontally. There are four
areas of wind that are measured: direction,
speed, character (gusts and squalls), and
shifts. Surface winds are measured by wind vanes
The calculation of temperature that takes into
consideration the effects of wind and
temperature on the human body. Describes the
average loss of body heat and how the
temperature feels. This is not the actual air
temperature. For an example, check out the wind
The direction from which the wind is blowing.
For example, an easterly wind is blowing from
the East, not toward the East. It is reported
with reference to true north, or 360 degrees on
the compass, and expressed to the nearest 10
degrees, or to one of the 16 points of the
compass (N, NE, etc.).
The rate of the motion of the air on a unit of
time. It can be measured in a number of ways. In
observing, it is measured in knots, or nautical
miles per hour. The unit most often used in the
United States is miles per hour.
A type of humidity that considers the mass of
water vapor present per unit volume of space.
Also considered as the density of the water
vapor. It is usually expressed in grams per
An instrument which measures wind speed.
A system of estimating and reporting wind
speeds. It is based on the Beaufort Force or
Number, which is composed of the wind speed, a
descriptive term, and the visible effects upon
land objects and/or sea surfaces. The scale was
devised by Sir Francis Beaufort (1777-1857),
hydrographer to the British Royal Navy.
A temperature scale where water at sea level has
a freezing point of 0 degrees C (Celsius) and a
boiling point of +100 degrees C. More commonly
used in areas that observe the metric system of
measurement. Created by Anders Celsius in 1742.
Same as Centigrade. In 1948, the Ninth General
Conference on Weights and Measures replaced
"degree centigrade" with "degree Celsius."
The process by which water vapor undergoes a
change in state from a gas to a liquid. It is
the opposite physical process of evaporation.
The dew point is the temperature at which dew
would form assuming all other conditions
remained the same. The dew point is a function
of the air temperature and humidity. The dew
point temperature can never be higher than the
air temperature. If the dew point temp and air
temp are the same, than the humidity would be
The dew point
is a very good measure of comfort. If the dew
point is high, the temperature and humidity must
also be high, and you are probably sweating
profusely even while standing still. If the dew
point is low, then either the temperature or
humidity or both are very low, and you are
feeling quite comfortable. This is a better
gauge for comfort than temperature or humidity
alone. It could be quite warm but very dry (low
dew point) and you would feel comfortable. It
could also be very humid but cool or cold (low
dew point) and you would feel comfortable. The
temperature to which air must be cooled at a
constant pressure to become saturated.
A thermometer used to measure the ambient
temperature. The temperature recorded is
considered identical to air temperature. One of
the two thermometers that make up a psychrometer.
The physical process by which a liquid, such as
water, is transformed into a gaseous state, such
as water vapor. It is the opposite physical
process of condensation.