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Temperature is a physical property of matter that

quantitatively expresses the common notions ofhot and cold. Objects of low temperature are

cold, while various degrees of higher temperatures are referred to as warm or hot. Heat

spontaneously flows to bodies of lower temperature. No net heat will be exchanged

Pressure (the symbol: P) is the force per unit area applied in a

direction perpendicular to the surface of an object. Gauge pressure (also spelled gage

pressure)[a]

is the pressure relative to the local atmospheric or ambient pressure.

Wind speed, or wind velocity, is a fundamental atmospheric rate.

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Wind speed affects weather forecasting, aircraft and maritime operations, construction projects,

growth and metabolism rate of many plant species, and countless other implications.[1]

Winddirection is reported by the direction from which it

originates. For example, a northerlywind blows from the north to the south.[1] Wind direction isusually reported in cardinal directions or in azimuth degrees. So, for example, a wind coming

from the south is given as 180 degrees; one from the east is 90 degrees.

Humidity is a term for the amount ofwater vapor in

the air, and can refer to any one of several measurements of humidity. Formally, humid air is

not "moist air" but a mixture of water vapor and other constituents of air, and humidity is

defined in terms of the water content of this mixture, called the Absolute humidity.[1]

In

everyday usage, it commonly refers to relative humidity, expressed as a percent in weather

forecasts and on household humidistats; it is so called because it measures the current absolute

humidity relative to the maximum. Specific humidityis a ratio of the water vapor content of the

mixture to the total air content (on a mass basis). The water vapor content of the mixture can

be measured either as mass per volume or as a partial pressure, depending on the usage.

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In meteorology, visibility is a measure of the distance at

which an object or light can be clearly discerned. It is reported within surface weather

observations and METAR code either in meters or statute miles, depending upon the country.

Visibility affects all forms of traffic: roads, sailing and aviation. Meteorological visibility refers totransparency of air: in dark, meteorological visibility is still the same as in daylight for the same

air.