Dew point and humidity

How Humid Is It? Simple Conversion Between Relative Humidity And Dew Point In Moist Air describes a simple rule of thumb for converting between dew point and humidity – when the humidity is above 50% (i.e. not for our high desert conditions). This is that there is 5% relative humdity change for every degree Celsius.

if it is 30 °C outside, and the relative humidity is 75%, then the dew point temperature will be about 25 °C. It’s also easy to see how much could be gained from evaporative cooling – in this case, at most 5 degrees. “Further, by adjusting the relationship a little to account for the effects of temperature, it is also simple to use the relative humidity to compute the altitude of cumulus cloud bases without a calculator to a good approximation, usually within about 10%”, says Lawrence.

In the first example, going from 75% to 100% is a change of 25% which means 5 degrees Celsius. In the second, you need to know that there is a temperature drop (the lapse rate) of about 6.5 degrees C for every 1000 meters.

Another interesting article about what temperature, altitude, and humidity do to bullet trajectories is at Lilja Precision Rifle Barrels – Articles: Ballistic Effects of Altitude, Temperature and Humidity

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