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The dew point of a given body of air is the temperature to which it must be cooled to become saturated with water vapor. This temperature depends on the pressure and water content of the air. When the air is cooled below the dew point, its moisture capacity is reduced and airborne water vapor will condense to form liquid water known as dew. [1]
The formula below approximates the heat index in degrees Fahrenheit, to within ±1.3 °F (0.7 °C). It is the result of a multivariate fit (temperature equal to or greater than 80 °F (27 °C) and relative humidity equal to or greater than 40%) to a model of the human body.
The dry-bulb temperature (DBT) is the temperature of air measured by a thermometer freely exposed to the air, but shielded from radiation. [1] The dry-bulb temperature is the temperature that is usually thought of as air temperature, and it is the true thermodynamic temperature.
The wet-bulb temperature is the lowest temperature that may be achieved by evaporative cooling of a water-wetted, ventilated surface.. By contrast, the dew point is the temperature to which the ambient air must be cooled to reach 100% relative humidity assuming there is no further evaporation into the air; it is the temperature where condensation (dew) and clouds would form.
The difference between the dry adiabatic lapse rate and the rate at which the dew point drops is around 4.5 °C per 1,000 m. Given a difference in temperature and dew point readings on the ground, one can easily find the LCL by multiplying the difference by 125 m/°C.
When the temperature is 30 °C (86 °F) and the dew point is 15 °C (59 °F), the humidex is 34. If the temperature remains 30 °C (86 °F) and the dew point rises to 25 °C (77 °F), the humidex rises to 42. The humidex is higher than the U.S. heat index at equal temperature and relative humidity. The humidex formula is as follows: [7] [8]
Xchanger Inc, webpage Calculator for humidity, dew point, mass flows & heat flux for variable pressure systems with compressors, blowers, vacuum pumps and heat exchangers. Corwin's Calculators Calculator for humidity, dew point. How to read and use a psychrometric chart; Free Online Interactive Psychrometric Chart
The NWS office in Tulsa, Oklahoma, in conjunction with Oral Roberts University's mathematics department, published an approximation formula to the WBGT that takes into account cloud cover and wind speed; in limited experimentation (four samples), the office claimed the estimate was regularly accurate to within 0.5 °F (0.28 °C), even with a ...