💧 Dew point
--°C
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The temperature at which air becomes saturated and dew forms — the truest measure of how humid and 'muggy' the air feels.
The dew point is the temperature to which air must cool for it to become fully saturated with water vapour and for dew, fog or cloud to begin forming. Unlike relative humidity, which changes with temperature, the dew point is an absolute measure of how much moisture is actually in the air — which makes it the single best indicator of how humid and 'muggy' it will feel.
Air can hold a certain maximum amount of water vapour, and warmer air can hold more. The dew point is the temperature at which the air you are breathing would be completely full. A high dew point means there is a lot of moisture in the air right now; a low dew point means the air is dry, regardless of what the thermometer reads.
Relative humidity is the amount of moisture in the air as a percentage of the maximum it could hold at that temperature — so it rises and falls as the air warms and cools through the day, even when the actual moisture is unchanged. The dew point stays steady as long as the moisture content does, which is why meteorologists prefer it for judging comfort and the chance of fog or storms.
When a surface or a parcel of air cools to the dew point, water vapour condenses into liquid. On the ground this makes dew or frost; in the air it makes fog or cloud. This is why fog often forms on clear, calm nights as the ground radiates heat away and the air just above it cools to its dew point.
Dew point is measured directly with a chilled-mirror hygrometer, which cools a mirror until condensation appears, or calculated from temperature and relative humidity readings taken by standard weather instruments. The value on this page is derived from a forecast model's temperature and humidity fields.
Below about 13°C feels pleasant and dry to most people. From 16°C it becomes noticeably humid, and above 21°C the air feels oppressive and sticky.
No. The dew point can equal the air temperature — that is when relative humidity is 100% and fog or dew forms — but it can never exceed it.
Relative humidity changes as the air warms and cools, so 70% humidity can feel very different at different temperatures. The dew point directly reflects the actual moisture, so it is a more reliable comfort guide.
Not on its own, but a high dew point means abundant moisture is available, which can fuel heavier showers and thunderstorms if other conditions trigger them.